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Grant Thornton Uk Software Engineer Interview Guide

Grant Thornton Uk Software Engineer interview guide: reported rounds, questions and how candidates describe the process.

The 60-second brief

A Software Engineer at Grant Thornton UK plays a critical role in bridging the gap between sophisticated financial services and modern technology. Unlike traditional tech companies, engineering here focuses on building robust, secure, and highly scalable enterprise-grade applications that power audit, tax, and advisory services. The tools you develop directly impact how the firm analyzes financial data, automates complex regulatory compliance workflows, and delivers strategic insights to thousands of clients across the globe. In this role, you will work on a mix of internal platforms, data analytics engines, and client-facing digital products. Because Grant Thornton UK operates in a highly regulated industry, software engineering is not just about writing clean code; it is about designing systems with security, data privacy, and accuracy at their core.

This guide is scoped to a Software Engineer candidate at Grant Thornton Uk.

Focus areas

  • Situational judgment
  • Quantitative reasoning (Math)
  • Communication

The Grant Thornton Uk interview process

Grant Thornton Uk candidates report 5 rounds over 4-6 weeks. The stages below are what candidates describe, not a published process.

Online Application

Submit your application for the Software Engineer position.

What to demonstrate

  • Submit your application for the Software Engineer position
  • Depth in Situational judgment

How to prepare

  • Answer aloud and timed: How do you ensure data security and privacy when designing an API that handles sensitive financial information?
  • Answer aloud and timed: Explain the differences between relational and non-relational databases, and how you would choose between them for a high-transaction audit platform.

Cognitive Tests

Complete online cognitive and situational judgment tests assessing reasoning and behavioral responses.

What to demonstrate

  • Complete online cognitive and situational judgment tests assessing reasoning and behavioral responses
  • Depth in Situational judgment

How to prepare

  • Answer aloud and timed: Walk me through your preferred testing strategy for a microservices-based application.
  • Answer aloud and timed: How do you handle concurrency and race conditions in a multi-user enterprise system?

Phone Interview with HR

Participate in a structured phone interview with HR to discuss your background.

What to demonstrate

  • Participate in a structured phone interview with HR to discuss your background
  • Depth in Situational judgment

How to prepare

  • Answer aloud and timed: Describe a time when you had to optimize a slow-performing database query or system bottleneck.
  • Answer aloud and timed: Describe a situation where you had to work with a difficult stakeholder or team member. How did you resolve the conflict?

Technical Video Interview

Engage in a detailed technical video interview to evaluate your technical skills.

What to demonstrate

  • Engage in a detailed technical video interview to evaluate your technical skills
  • Depth in Situational judgment

How to prepare

  • Answer aloud and timed: How do you prioritize your tasks when working under tight deadlines with competing project requirements?
  • Answer aloud and timed: Tell me about a time you made a technical mistake. How did you identify it, and what did you do to rectify the situation?

Final Assessment Stage

Take part in a collaborative group activity and an individual conversation-style interview.

What to demonstrate

  • Take part in a collaborative group activity and an individual conversation-style interview
  • Depth in Situational judgment

How to prepare

  • Answer aloud and timed: How do you keep your technical skills up to date, and how have you applied a newly learned technology to a recent project?
  • Answer aloud and timed: Describe a time when you had to explain a complex technical concept to a non-technical business stakeholder.

Where candidates lose points

Structure your behavioral answers

Use the STAR method (Situation, Task, Action, Result) to keep your answers structured and concise. Focus heavily on the Action you took and the Result of your efforts.

Practice active collaboration

In the group exercise, remember that you are not competing against the other candidates in the room. You are being assessed on how well you work with them. Build on their ideas, encourage quieter members to speak, and help keep the group focused on the objective.

Abandoning working code to chase the optimal solution

Get the straightforward version correct, state its complexity, and only then optimise, keeping the working version until the faster one passes the same cases. A correct quadratic solution with a stated path to linear beats a half-written optimal one that never ran.

Questions & practice

How do you handle concurrency and race conditions in a multi-user enterprise system?

Medium · Technical & System Design

Approach

  1. Say what the runtime actually does before reasoning about the code.
  2. Name what is shared across threads and what owns each piece of state.
  3. Identify the window where an invariant is briefly untrue.
  4. Distinguish a value from a reference to it, and say which one you handed out.

Follow-up

  • What happens if two callers reach this at the same time?
  • Where could this allocate more than you expect?

Archive a resource graph without breaking live references or recursing

Medium · graph traversal · topological order · tenant isolation

Resources reference other resources within a tenant; for the largest tenant the reference table holds up to 2,000,000 nodes and 8,000,000 edges. Archiving a resource must archive everything reachable from it that nothing outside the set still references, refuse when a live external referrer exists, and terminate when references form cycles, which they legitimately do. Produce the archive order and the refusal list, targeting O(V+E). Say what stops the traversal crossing a tenant boundary, and why recursion is the wrong control structure at this size.

Approach

  1. Load the subgraph with the tenant predicate on both endpoints of the edge, not only on the side you started from. Scoping the left table alone is the classic cross-tenant leak: one mis-entered edge then pulls another tenant's resources into the traversal and, worse, into the archive.
  2. Traverse iteratively with an explicit stack. A 2,000,000-node graph can hold a chain deep enough to exhaust a native stack in the low tens of thousands of frames, and that failure is a process crash rather than an error you can return.
  3. Treat cycles as data rather than corruption: compute strongly connected components with Tarjan in O(V+E) using its own explicit stack, then condense. The condensation is a DAG, so a topological order over it gives the archive order, and every member of a component archives in one transaction because no order within a cycle is valid.
  4. Decide refusals with reverse edges. A candidate is archivable only if every in-edge originates inside the candidate set, so build the transpose or count in-degrees restricted to the visited set, and emit each blocked resource with the id of the external referrer, which is the only part of the answer an operator can act on.

Follow-up

  • The graph is read in one query and the archive writes a minute later. What can change in between, and how do you make the write safe?
  • The candidate set is 400,000 resources. Is that one transaction, and if not, what does a half-finished archive look like to a reader?

Diff a projection against the primary without per-row point reads

Hard · reconciliation · range hashing · throttling

The listing projection has drifted and some rows show a stale version. The primary holds 40,000,000 resource rows across 12,000 tenants while serving 1,200 writes and 14,000 reads per second. The obvious repair, reading each resource row and comparing its version against the projection, is correct and would eventually finish. Explain precisely why it is unacceptable here, then give a diff that finds the differing rows, state its complexity, and make it safe to run against a live primary. Replication lag is usually under 100 ms and is not bounded.

Approach

  1. Quantify the naive cost rather than calling it slow: 40,000,000 point reads at even 0.5 ms each is over five hours serialised, and the only lever is concurrency, which is exactly what you cannot spend. The primary's pool is sized for the write path, and 40,000,000 random reads evict the buffer cache that sustains the 85 percent cache hit rate, so the audit degrades the system it is auditing.
  2. Replace random access with one ordered pass per side. Both sides can be read in (tenant_id, resource_id) order, which is a sequential scan on each and a merge join in O(n) time and O(1) memory. For a dense diff that is the whole answer, and it reads the primary once instead of 40,000,000 times.
  3. For the expected sparse case, compare range hashes instead of rows: partition the key space, compute per range an order-independent aggregate over hash(resource_id, version), compare aggregates, and descend only into ranges that differ. With d differing rows and branching factor B, at most d ranges mismatch per level, so the drill-down examines O(d log_B(n/d)) ranges and reads full rows only in mismatching leaves.
  4. Aggregate with a sum modulo 2^64 or a multiset hash, never XOR. XOR is order-independent but self-cancelling, so two rows wrong in the same way, or a row duplicated on one side, leave the range aggregate matching and the range is declared clean.

Follow-up

  • The diff reports 900 stale rows. How do you decide between patching those rows and rebuilding the projection from resource_revision?
  • Same job, but the projection lives in a search index that cannot be scanned in key order. What changes?

Explain why the owner filter ignores the listing index

Medium · composite index · query plans · sort elimination

The only index on resource is (tenant_id, status, updated_at DESC, resource_id DESC). A new endpoint returns one user's resources across all statuses, newest created first: WHERE tenant_id = $1 AND owner_user_id = $2 ORDER BY created_at DESC LIMIT 20. On a tenant with 2M rows it takes 900 ms and EXPLAIN shows a sort above a large scan. Explain precisely why the existing index cannot serve it, give the index that can, and state which of these the new index still will not help: owner_user_id alone across tenants; the same query ordered by updated_at. PostgreSQL 16.

Approach

  1. Separate the two jobs an index does. For filtering, a composite btree is seekable only on a left prefix, so with no predicate on status the scan can at best range over tenant_id and test owner_user_id per row; PostgreSQL 16 has no btree skip scan to jump the unconstrained column.
  2. For ordering, the index is sorted by (status, updated_at) within a tenant and not by created_at, so the LIMIT cannot stop early: every matching row is read and then sorted. That is the 'Sort Method: top-N heapsort' line, and it is why the plan reads 2M rows to answer with 20.
  3. Derive the replacement from the access path — equality, equality, then the ordering column: CREATE INDEX CONCURRENTLY ON resource (tenant_id, owner_user_id, created_at DESC). The scan seeks to the (tenant, owner) range and walks 20 entries in order, so the Sort node disappears along with the row-read.
  4. Treat INCLUDE (title, status) as conditional, not free. An index-only scan still visits the heap for any row whose page is not marked all-visible, so on a table taking 1.2k writes/second the win depends on autovacuum keeping the visibility map current, and the wider index costs more on every insert.

Follow-up

  • 90% of rows are status='active'. Would a partial index WHERE status = 'active' change your answer, and for which of the three queries?
  • A dashboard runs this for 40 owners in one page load. What changes about the design?

Write the update path that detects a concurrent edit

Medium · optimistic concurrency · transactional outbox · audit history

resource carries version INT NOT NULL DEFAULT 1. resource_revision holds revision_id, resource_id, version, actor_user_id, change_kind, patch JSONB, request_id, created_at with UNIQUE (resource_id, version). outbox_event holds aggregate_type, aggregate_id, aggregate_version, event_type, payload, status. A PUT carries the version the client read. Write the exact statements for the single transaction that applies the edit, records the revision and enqueues 'resource.updated', and give the handler's branch on zero affected rows. Then say what PostgreSQL 16 does under READ COMMITTED when two of these updates hit one row at once.

Approach

  1. One transaction, three writes, no network call inside it: UPDATE resource SET title = $3, version = version + 1, updated_at = now() WHERE resource_id = $1 AND tenant_id = $4 AND version = $2; then INSERT the resource_revision row at version $2 + 1; then INSERT the outbox_event row at the same aggregate_version. The event goes to a table rather than a broker because no transaction spans both.
  2. Branch on the affected-row count before doing anything else. Zero has three causes — stale version, wrong tenant, row gone — so re-read once and map to 409 carrying the current version, or 404 for an id outside the caller's tenant, which also stops the endpoint confirming that another tenant's id exists.
  3. State the engine behaviour instead of assuming it. Under READ COMMITTED the second UPDATE blocks on the row lock, and when the first commits PostgreSQL re-evaluates the WHERE clause against the newly committed row, so the version predicate now fails and the statement reports zero rows. Under REPEATABLE READ the identical collision raises SQLSTATE 40001 instead, so the handler must fold both shapes into one conflict response.
  4. Keep UNIQUE (resource_id, version) even though the predicate already serialises writers. It is what makes a lost update unwritable if any other path ever reaches the revision table, and it converts a logic bug into 23505 rather than into a silently missing history row.

Follow-up

  • A client sends the version it read ten minutes ago and the resource has moved three versions. What is in your 409 so it can resolve the conflict without a full re-fetch?
  • Two editors, two disjoint fields, no overlap. Does your answer still refuse the second write, and should it?

How do you ensure data security and privacy when designing an API that handles sensitive financial information

Medium · Technical & System Design

How do you ensure data security and privacy when designing an API that handles sensitive financial information?

Approach

  1. Say who the caller is and what they do when the call fails halfway.
  2. Define the identity of a request so a retry cannot double-apply it.
  3. Separate accepted, pending, failed and confirmed; they are different facts.
  4. Design the error taxonomy before the success shape; callers branch on it.

Follow-up

  • What happens if the caller retries after a timeout?
  • How does a client discover it is on an old version of this contract?

Explain the differences between relational and non-relational databases, and how you would choose between them

Medium · Technical & System Design

Explain the differences between relational and non-relational databases, and how you would choose between them for a high-transaction audit platform.

Approach

  1. Fix the scope first: who calls this, how often, and what they do when it fails.
  2. Name the read and write paths separately; they rarely have the same bottleneck.
  3. Choose a partition key and say what query it makes expensive.
  4. State the consistency you need, and where you are willing to be stale.

Follow-up

  • What breaks first when traffic grows ten times?
  • How does this behave when that dependency is down for an hour?

Walk me through your preferred testing strategy for a microservices-based application.

Medium · Technical & System Design

Approach

  1. Fix the scope first: who calls this, how often, and what they do when it fails.
  2. Name the read and write paths separately; they rarely have the same bottleneck.
  3. Choose a partition key and say what query it makes expensive.
  4. State the consistency you need, and where you are willing to be stale.

Follow-up

  • What breaks first when traffic grows ten times?
  • How does this behave when that dependency is down for an hour?

If a critical production bug is discovered right before a major client presentation, what immediate steps do y

Medium · Situational Judgment & Logic

If a critical production bug is discovered right before a major client presentation, what immediate steps do you take?

Approach

  1. Clarify what is being asked and what a complete answer contains.
  2. State your assumptions explicitly before working the problem.
  3. Say what you would check first and why it is the highest-information step.
  4. Work from the requirement backwards to the design.

Follow-up

  • What assumption would you test first?
  • How would you know your answer was wrong?

How do you approach a complex problem when you do not have all the necessary information or requirements?

Medium · Situational Judgment & Logic

Approach

  1. Clarify what is being asked and what a complete answer contains.
  2. State your assumptions explicitly before working the problem.
  3. Say what you would check first and why it is the highest-information step.
  4. Work from the requirement backwards to the design.

Follow-up

  • What assumption would you test first?
  • How would you know your answer was wrong?

Scenario-based: A team member is consistently missing deliverables, affecting the sprint goal. How do you addr

Medium · Situational Judgment & Logic

Scenario-based: A team member is consistently missing deliverables, affecting the sprint goal. How do you address this?

Approach

  1. Clarify what is being asked and what a complete answer contains.
  2. State your assumptions explicitly before working the problem.
  3. Say what you would check first and why it is the highest-information step.
  4. Work from the requirement backwards to the design.

Follow-up

  • What assumption would you test first?
  • How would you know your answer was wrong?

One customer endpoint stalls deliveries to every other destination

Medium · bulkhead · timeouts · saturation

The egress service delivers about 1.5k webhooks/second across 40,000 destinations, with a per-destination concurrency cap of 4 and a 10-second connect-plus-read timeout. Throughput falls to 300/second, queue depth climbs, and p99 delivery latency for unaffected destinations goes from 200 ms to minutes, while the error rate barely moves. One tenant holds 900 destination rows whose URLs share a hostname that now answers in 9.5 seconds. Explain the mechanism with the arithmetic, then give the containment in the order you would apply it.

Approach

  1. Look at saturation before errors. A flat error rate with collapsing throughput says nothing is failing, things are waiting, so the first signal to pull is in-flight request count or pool wait time rather than the error counter. This is the distinction that decides the whole investigation.
  2. Group in-flight work by resolved host, not by destination id. The cap is keyed per destination row, so 900 rows sharing one hostname buy 3,600 concurrent slots against a single host, each held for 9.5 seconds. The bulkhead was never a bulkhead for that host, and grouping by the wrong dimension is why the dashboard looked healthy.
  3. Do the arithmetic in both directions. Required concurrency is arrival rate times latency, so 1.5k/second at 200 ms needs about 300 in flight, which is entirely consumed by 3,600 slow slots; conversely whatever concurrency is left sustains rate equals concurrency divided by 9.5 seconds, which is the 300/second you are seeing. Matching both numbers is what promotes this from a plausible story to the mechanism.
  4. Explain why the circuit breaker never helped. It opens on consecutive failures, and a 9.5-second response inside a 10-second timeout is a success. Slow is not failing, so an error-rate breaker cannot see this; you need a slow-call ratio, a deadline propagated from the caller's remaining budget, or a concurrency limiter.

Follow-up

  • The host recovers to 80 ms. How long does the queue take to drain, and what does the drain do to the recovered host?
  • Where should the 10-second timeout number actually come from?

Suggested practice checklist

Built from the rounds and topics Grant Thornton Uk candidates report.

Day 1 — Map the Grant Thornton Uk loop

  • Write out the reported sequence: Online Application, Cognitive Tests, Phone Interview with HR, Technical Video Interview, Final Assessment Stage.
  • For each round, write one sentence on what it is judging, from the description above, and mark the one you are least ready for.

Deliverable: A one-page map of the 5 reported rounds, with the weakest marked.

Day 2 — Work Situational judgment

  • Spend the session on Situational judgment, which Grant Thornton Uk candidates report being tested on.
  • Write one worked example in Situational judgment and time yourself on it.

Deliverable: One timed worked example in Situational judgment.

Day 3 — Work Quantitative reasoning (Math)

  • Spend the session on Quantitative reasoning (Math), which Grant Thornton Uk candidates report being tested on.
  • Write one worked example in Quantitative reasoning (Math) and time yourself on it.

Deliverable: One timed worked example in Quantitative reasoning (Math).

Day 4 — Work Communication

  • Spend the session on Communication, which Grant Thornton Uk candidates report being tested on.
  • Write one worked example in Communication and time yourself on it.

Deliverable: One timed worked example in Communication.

Day 5 — Answer out loud: Technical & System Design

  • Answer aloud, timed: How do you ensure data security and privacy when designing an API that handles sensitive financial information?
  • Answer aloud, timed: Explain the differences between relational and non-relational databases, and how you would choose between them for a high-transaction audit platform.

Deliverable: Spoken answers to 2 reported Technical & System Design question(s), under time.

Day 6 — Answer out loud: Situational & Behavioral

  • Answer aloud, timed: Describe a situation where you had to work with a difficult stakeholder or team member. How did you resolve the conflict?
  • Answer aloud, timed: How do you prioritize your tasks when working under tight deadlines with competing project requirements?

Deliverable: Spoken answers to 2 reported Situational & Behavioral question(s), under time.

Day 7 — Answer out loud: Situational Judgment & Logic

  • Answer aloud, timed: If a critical production bug is discovered right before a major client presentation, what immediate steps do you take?
  • Answer aloud, timed: How do you approach a complex problem when you do not have all the necessary information or requirements?

Deliverable: Spoken answers to 2 reported Situational Judgment & Logic question(s), under time.

Behavioural preparation

Behavioural rounds judge the decision you made and what it cost.

Describe a time when you had to optimize a slow-performing database query or system bottleneck.

Medium · Technical & System Design

Approach

  1. Pick a story where you made the decision, not one where you watched it.
  2. State the situation in two sentences and spend the rest on the reasoning.
  3. Give the blast radius: what could have broken, and what you measured.
  4. Name the disagreement and how you resolved it with evidence.

Follow-up

  • What would you do differently if you ran that again?
  • How did you know your change caused the improvement?

Describe a situation where you had to work with a difficult stakeholder or team member. How did you resolve th

Medium · Situational & Behavioral

Describe a situation where you had to work with a difficult stakeholder or team member. How did you resolve the conflict?

Approach

  1. Pick a story where you made the decision, not one where you watched it.
  2. State the situation in two sentences and spend the rest on the reasoning.
  3. Give the blast radius: what could have broken, and what you measured.
  4. Name the disagreement and how you resolved it with evidence.

Follow-up

  • What would you do differently if you ran that again?
  • How did you know your change caused the improvement?

How do you prioritize your tasks when working under tight deadlines with competing project requirements?

Medium · Situational & Behavioral

Approach

  1. Pick a story where you made the decision, not one where you watched it.
  2. State the situation in two sentences and spend the rest on the reasoning.
  3. Give the blast radius: what could have broken, and what you measured.
  4. Name the disagreement and how you resolved it with evidence.

Follow-up

  • What would you do differently if you ran that again?
  • How did you know your change caused the improvement?

Tell me about a time you made a technical mistake. How did you identify it, and what did you do to rectify the

Medium · Situational & Behavioral

Tell me about a time you made a technical mistake. How did you identify it, and what did you do to rectify the situation?

Approach

  1. Pick a story where you made the decision, not one where you watched it.
  2. State the situation in two sentences and spend the rest on the reasoning.
  3. Give the blast radius: what could have broken, and what you measured.
  4. Name the disagreement and how you resolved it with evidence.

Follow-up

  • What would you do differently if you ran that again?
  • How did you know your change caused the improvement?

How do you keep your technical skills up to date, and how have you applied a newly learned technology to a rec

Medium · Situational & Behavioral

How do you keep your technical skills up to date, and how have you applied a newly learned technology to a recent project?

Approach

  1. Pick a story where you made the decision, not one where you watched it.
  2. State the situation in two sentences and spend the rest on the reasoning.
  3. Give the blast radius: what could have broken, and what you measured.
  4. Name the disagreement and how you resolved it with evidence.

Follow-up

  • What would you do differently if you ran that again?
  • How did you know your change caused the improvement?

Describe a time when you had to explain a complex technical concept to a non-technical business stakeholder.

Medium · Situational & Behavioral

Approach

  1. Pick a story where you made the decision, not one where you watched it.
  2. State the situation in two sentences and spend the rest on the reasoning.
  3. Give the blast radius: what could have broken, and what you measured.
  4. Name the disagreement and how you resolved it with evidence.

Follow-up

  • What would you do differently if you ran that again?
  • How did you know your change caused the improvement?