Senior Software Engineer Interview Questions UK: 8 Real Questions and What Interviewers Want

Applying for a Senior Software Engineer job in the UK? Here is what you are likely to be asked. These questions come from our Senior Software Engineer question bank of 25 questions, written for UK employers at senior level.

Eight Senior Software Engineer interview questions, and what the interviewer is thinking

1. Walk me through how you would design a system to handle a sudden tenfold increase in traffic.

Why they ask: System design is central to senior interviews, testing whether you reason methodically about scale and trade-offs.

2. When would you choose microservices over a monolith, and when would you advise against it?

Why they ask: Architectural judgement and resisting fashion are key senior skills.

3. What does being a senior engineer mean to you, beyond writing good code?

Why they ask: They want to see that you understand the leadership, influence and multiplier aspects of the role.

4. How do you approach code reviews, both as a reviewer and an author?

Why they ask: Code review culture is a core senior responsibility, and they want to see maturity, not nitpicking.

5. You deploy a release on Friday afternoon and error rates spike in production. What do you do?

Why they ask: Incident response under pressure shows judgement, leadership and operational maturity.

6. How do you decide where to use eventual consistency, and how do you handle distributed transactions across services?

Why they ask: Distributed data consistency is a tough area, and seniors are expected to understand the trade-offs.

7. Your product manager wants a feature in two weeks, but you estimate five weeks to do it properly. What do you do?

Why they ask: Negotiating scope and quality with stakeholders is a classic senior challenge.

8. Tell me about a significant technical decision you led, including how you built consensus.

Why they ask: Senior engineers are judged on technical judgement and the ability to bring others with them.

A sample answer to question 1

Walk me through how you would design a system to handle a sudden tenfold increase in traffic.

I'd start by clarifying what we mean: read or write heavy, which parts are the bottleneck, and our latency and availability targets. Then I'd work from the edge inwards. Put a CDN in front for static and cacheable content, and use a load balancer with autoscaling stateless application instances, which means externalising sessions to something like Redis. The database is usually the real constraint, so I'd add read replicas, caching with sensible TTLs, and connection pooling, and look at query efficiency before reaching for sharding, which adds big complexity. For write spikes, I'd decouple with queues, such as Kafka or SQS, so we absorb bursts and process at a steady rate, accepting eventual consistency where the business can tolerate it. I'd protect the system with rate limiting, timeouts, circuit breakers and graceful degradation, for example turning off non-essential features. I'd validate all this with load tests, such as k6, before the event, and make sure observability and alerting are in place. Finally, I'd do a cost check, as scaling isn't free.

Common mistake to avoid: Jumping to microservices or sharding immediately; Ignoring observability and cost

Want the rest?

Full model answers, key points and common mistakes for all 25 questions are on the Senior Software Engineer interview questions page. The first five are free, no sign-up needed.