Choosing a Software Development Agency in London: 12 Questions to Ask

London has hundreds of software development agencies. Rates range from £300 to £900+ per day. Quality varies enormously. Choosing the wrong agency doesn't just waste money — it can set your project back by 12–18 months, erode internal trust in technology, and in the worst cases result in unusable software.

After 15 years delivering software projects, we've seen what goes wrong when clients choose the wrong partner. We've also inherited several half-finished projects from other agencies. Here are the 12 questions we'd ask if we were in your position.

1. Can you show me production code from a recent project?

Most agencies will show you polished case study pages with impressive screenshots. That's marketing, not evidence. What you actually want to see is a GitHub repository, a code review, or at minimum a technical walkthrough of a real system they built.

You don't need to be a developer to do this — bring a technical advisor or CTO for 30 minutes. What you're looking for: is the code readable? Does it have tests? Is it documented? Is there a sensible structure?

Good agencies welcome this question. Weak agencies deflect it.

2. Who exactly will be working on my project?

Many agencies sell you the senior partners in the pitch room, then hand the actual work to junior developers or subcontractors. This isn't necessarily bad — junior developers can do excellent work — but you should know the real team composition upfront.

Ask: Will the developers I meet today be the ones writing my code? What percentage of your work is done in-house vs. subcontracted? Can I meet the lead developer before we sign?

The answers will tell you a lot about how the agency operates.

3. How do you handle scope changes?

Scope changes are inevitable. Requirements evolve as users provide feedback, business conditions change, or you simply discover you need something different from what you originally specified. The question isn't whether scope will change — it's how the agency handles it when it does.

Red flags: agencies that say "we'll deal with that in the contract" without explaining their process, or agencies that present change requests as entirely separate projects with new pricing from scratch.

Green flags: a clear change request process, transparent pricing for additions, willingness to deprioritise lower-value features to make room for higher-value ones within budget.

4. What does your testing process look like?

Untested code is technical debt in disguise. Ask specifically: do you write unit tests? Integration tests? End-to-end tests? What's your test coverage target?

You should also ask about QA processes: is there a dedicated QA engineer on the project, or does the developer test their own code? Is there a staging environment where you can test before production deploys?

There is no single correct answer to all of these — different project types warrant different testing strategies. But agencies that can't articulate their testing approach clearly are likely not practising one consistently.

5. How will you communicate progress with me?

Communication failures are the #1 cause of project dissatisfaction in software development. Not technical failures — communication failures.

Ask: How often will I receive written updates? What project management tool do you use, and will I have access? How quickly can I expect a response if I spot an issue? Will there be a regular call, and how long will it be?

Our approach: weekly written status updates, a Notion or Linear project board the client can access anytime, a 30-minute weekly call during active sprints, and a Slack channel for day-to-day questions. You should expect something similar from any serious agency.

6. Who owns the code when the project ends?

This seems like a legal formality, but it has real practical implications. If you don't own the IP outright, you may be locked into the agency for future changes, or face licensing complications if you sell the business.

The standard for client-funded custom development is: you own 100% of the code, IP, and any data the system generates. Get this in writing. Any agency that hedges on this question is a risk.

7. Can you show me a reference from a client in a similar industry?

Case studies on a website are curated. A live reference call with a past client is unfiltered. Ask for one.

Specifically, ask to speak with a client who had a challenging project — one that had scope changes, technical difficulties, or deadline pressures. How an agency behaves under pressure is more revealing than how they perform on clean, well-scoped projects.

If an agency struggles to provide even one reference, that's a significant warning sign.

8. What happens when a developer leaves your team mid-project?

Turnover happens, especially in the London tech market. Developer attrition mid-project is a real risk, and agencies should have a clear answer for how they handle it.

What you want to hear: documentation practices that ensure knowledge isn't siloed in one developer's head, an onboarding process for replacement developers, and a commitment to maintaining continuity for the client.

Bonus points if they have low turnover and can tell you their average developer tenure — experienced agencies often have developers who've been with them for years.

9. How do you approach security and data protection?

For UK businesses, GDPR compliance isn't optional. For healthcare or financial services, there are further requirements (NHS Digital standards, FCA rules). Ask the agency how they handle:

• Authentication and authorisation (how they prevent unauthorised access)
• Data encryption at rest and in transit
• GDPR data processing agreements
• Secrets management (how API keys and credentials are stored)
• Penetration testing (do they offer this, or recommend third parties?)

A developer who can't explain at least the basics of OWASP Top 10 vulnerabilities should not be building production software for your business.

10. What is your post-launch support structure?

Launch is not the end — it's the beginning of a new phase. Bugs will emerge in production that didn't appear in testing. Users will do things you didn't anticipate. Performance may degrade under real load.

Ask: is there a warranty period after launch during which bugs are fixed at no extra charge? What are your maintenance retainer options? What is your average response time for production issues?

Agencies that disappear after launch delivery are common. Agencies that treat post-launch support as a continuation of the relationship are rarer and more valuable.

11. How do you stay current with new technology?

The software landscape changes rapidly. AI tooling in particular has transformed what's possible in the last two years. An agency that was excellent in 2020 but hasn't evolved may be teaching you outdated patterns.

You're not looking for an agency that chases every new framework. You're looking for one that has a considered view on when to adopt new technology and when to stick with proven approaches.

Ask how they decided to adopt (or not adopt) specific technologies: Next.js App Router, TypeScript, Tailwind, serverless, AI APIs. Their reasoning will reveal their engineering culture.

12. What would you do differently if you were us?

This is the most revealing question. It invites the agency to be constructively critical — to push back on your assumptions, suggest alternatives, or surface risks you haven't considered.

Good agencies will have an opinion. They'll say things like: "I'd suggest validating this assumption with 10 user interviews before we build anything" or "Your timeline seems optimistic for this scope — have you considered phasing it differently?" or "We could save £20,000 by using this existing open-source tool for that feature."

Agencies that validate everything you've said without reservation are either desperate for the work or not thinking hard about your problem. Neither is what you want.

Red Flags to Watch For

Beyond the questions above, here are patterns that should make you hesitate:

• Unusually low quotes — if an agency is 50%+ cheaper than everyone else, ask why
• Reluctance to provide a detailed, written proposal with assumptions clearly stated
• Promising unrealistic timelines ("we can build that in 2 weeks") without detailed scope
• No examples of completed projects in your industry or project type
• Overpromising on AI capabilities without demonstrating real implementation experience
• Pressure to sign before you've had time to do due diligence
• Senior people present at the pitch but unavailable to answer technical questions

The Right Agency for You

The best agency isn't necessarily the most expensive, or the one with the most awards, or even the one with the slickest website. It's the one that understands your domain, communicates clearly, delivers what they promise, and treats your project as if it were their own product.

Use these 12 questions as a filter. The agencies that answer them well and invite further scrutiny are the ones worth trusting with your project.