What UK Interviewers Are Really Assessing
Graduate software engineering interviews in the UK test three things simultaneously: technical ability (can you solve the problem?), communication (can you explain your thinking?), and potential (will you grow quickly in this role?). Strong answers demonstrate all three, not just correctness.
This guide covers the most frequently asked question types with model answers you can adapt. For a complete preparation plan, also read our guide on how to prepare for coding interviews.
Technical Questions - Concepts and Theory
"What is the difference between a stack and a queue?"
What they're testing: Foundational data structure knowledge.
Model answer: "A stack is a Last-In-First-Out (LIFO) structure - the last element added is the first removed. A queue is First-In-First-Out (FIFO) - the first element added is the first removed. Stacks are typically used for function call management, undo operations, and depth-first search. Queues are used for breadth-first search, task scheduling, and message passing systems. In Python, you'd implement a stack with a list using append and pop, and a queue with collections.deque using append and popleft for O(1) operations at both ends."
"Explain the difference between time complexity and space complexity."
What they're testing: Whether you can reason about algorithmic efficiency.
Model answer: "Time complexity measures how the number of operations an algorithm performs grows as the input size increases. Space complexity measures how much additional memory it requires. For example, a nested loop iterating over an array has O(n²) time complexity. If that loop only uses a constant number of extra variables, it has O(1) space complexity. The two are often in tension - you can frequently trade space for time, like using a hash map to reduce a two-pointer O(n²) search to O(n) at the cost of O(n) extra space."
"What is a RESTful API and what makes one well-designed?"
What they're testing: Web fundamentals knowledge - essential for most software engineering roles.
Model answer: "REST - Representational State Transfer - is an architectural style for APIs over HTTP. A well-designed REST API uses nouns for endpoints (not verbs), uses the correct HTTP methods (GET for reads, POST for creates, PUT/PATCH for updates, DELETE for removes), returns appropriate status codes (200 OK, 201 Created, 404 Not Found, 400 Bad Request), and is stateless - meaning each request contains all the information needed to process it. Good REST APIs also version themselves (e.g., /api/v1/) so breaking changes don't affect existing clients."
Coding Questions - Problem Solving
"Write a function that finds the two numbers in an array that sum to a target."
What they're testing: Problem solving, hash map usage, time complexity awareness.
Approach to explain out loud: "My first instinct is a brute-force O(n²) solution with nested loops, but I can do better. I'll use a hash map to store each number and its index as I iterate. For each element, I check whether its complement - target minus the current number - already exists in the map. If it does, I've found my pair. This gives O(n) time and O(n) space."
Key point for UK interviews: Always mention the brute force first, then optimise. This shows analytical thinking, not just memorised solutions.
"Reverse a linked list in place."
What they're testing: Pointer manipulation, ability to handle in-place operations without getting confused.
Approach: "I'll use three pointers: previous (initially null), current (head), and next. At each step: save next, point current's next to previous, move previous to current, and advance current to saved next. When current is null, previous is the new head. Time O(n), space O(1)."
System Design Questions (Entry Level)
"How would you design a URL shortener like bit.ly?"
What they're testing: Whether you can think through a system end-to-end. Graduate-level - don't panic.
Model answer structure:
- Clarify requirements: "Is this read-heavy or write-heavy? Do we need analytics? Is it global?" (shows you think before diving in)
- Core components: Client → API → Application server → Database
- Key decisions: "For the short code, I'd generate a random 6-character alphanumeric string (62⁶ = ~56 billion combinations). Store mappings in a key-value store like Redis for O(1) lookups. Use a SQL database for the original URLs, user data, and analytics. Serve GET requests through a CDN for speed."
- Scaling: "Read requests dominate, so I'd add caching at the API layer - most short URLs are clicked repeatedly in short windows."
Behavioural Questions
"Tell me about a project you're most proud of."
What they're testing: Communication, technical depth, what you care about.
Model structure (STAR): "During my final year, I built [project name] - [one sentence on what it does]. The technical challenge I enjoyed most was [specific problem]. I solved it by [approach], which meant [outcome or result]. I'm proud of it because [genuine reason - e.g., people actually use it / I learned X / I built it completely independently]."
Mistake to avoid: Describing a project at a very high level without any technical substance. Interviewers want to see you go deep on one aspect, not summarise everything you did.
"Describe a time you had a disagreement with a teammate."
What they're testing: Collaboration, maturity, communication under friction.
Model answer: "In my second year group project, a teammate wanted to use a NoSQL database while I believed a relational schema was better suited to our data model. Rather than arguing my position, I suggested we each write a brief doc outlining the trade-offs and then discuss as a team. Once we saw both arguments written down, the team agreed that the relational model was a better fit - but my teammate's point about schema flexibility made us add a JSONB column for metadata, which turned out to be genuinely useful."
Questions to Ask at the End
Always prepare 2–3 thoughtful questions. Good options for graduate software engineering roles:
- "What does the onboarding process look like for a new graduate engineer?"
- "How does the team handle code reviews - what does a typical PR process look like?"
- "What's the biggest technical challenge the team is working through right now?"
Prepare Company-Specifically
Generic preparation only takes you so far. The most effective thing you can do before a specific interview is understand what that company actually tests. GradSignal's interview playbooks give you the exact questions, LeetCode patterns, and stage-by-stage breakdowns for UK tech companies - based on real candidate experiences. Use them before every interview.