How to Choose a .NET Development Company in London: What to Check Before Hiring

Choosing a .NET development company is a decision you'll live with for years. The partner you pick will shape how reliable, secure and maintainable your software is, and how easy it is to change later. This guide explains how to choose a .NET development company in London, or anywhere in the UK, step by step, with a scorecard you can use to compare companies side by side.

Get it right and you gain a team that understands your business and builds software that keeps working (see how we work on our .NET development services page). Get it wrong and you can end up with missed deadlines, code nobody else can maintain, or an application stuck on an unsupported version of .NET.

1. Start With Your Requirements

The most common reason software projects go wrong isn't poor coding. It's unclear requirements. Before contacting any .NET development agency in London, write a short brief covering:

• The problem: what isn't working today, and who it affects.
• The users: customers, staff, partners, or all three.
• Must-have features: what has to be in the first release.
• Systems to connect: for example Microsoft 365, Dynamics 365, Xero, Sage or a legacy database.
• Constraints: budget range, deadlines, and any rules you must follow, such as UK GDPR or sector regulations.
• What success looks like: for example, time saved per week, fewer errors or faster customer response.

Know which type of .NET project you have

Companies are often stronger at some types of .NET work than others:

2. Check .NET Technical Expertise (Without Being a Developer)

You don't need to read code to judge technical expertise. You need to ask questions that reveal whether a company keeps up with the platform.

Do they understand .NET versions and support?

Microsoft releases a new version of .NET every November. Even-numbered releases are Long Term Support (LTS) releases and odd-numbered releases are Standard Term Support (STS) releases (Microsoft .NET support policy).

This has real consequences. Microsoft has confirmed that .NET 8 and .NET 9 both reach end of support on 10 November 2026, after which they no longer receive security fixes, and recommends upgrading to .NET 10, an LTS release supported until November 2028 (.NET Blog, Microsoft).

Source: Microsoft .NET Blog. Check Microsoft's support policy page for the latest dates.

A good partner should be able to explain, in plain English:

• which .NET version they would use for your project, and why
• how they plan upgrades over the life of your application
• the difference between modern .NET and the older .NET Framework, which many existing business systems still run on

Do they cover the parts of .NET you need?

Ask about certifications, but don't rely on them

Microsoft certifications can show that developers have studied the platform. Ask to see them, and check they're current. But treat them as a supporting signal: delivered projects and how a team explains its decisions tell you more.

3. Review Portfolios and Case Studies Properly

Most portfolios look impressive. The skill is in asking the right follow-up questions. For each relevant project, ask:

1. What problem did the client have?
2. What exactly did your team build, and what did the client or other suppliers build?
3. Which .NET technologies and versions did you use?
4. What went wrong, and how did you handle it?
5. Is the system still live, and do you still support it?
6. Can I speak to the client?

Be cautious of case studies with no verifiable details, vague claims such as "improved efficiency" with no explanation, or reluctance to provide references.

4. Understand How They Build Software

A clear development process protects your budget and timeline. Ask the company to walk you through a typical project.

Strong signs

• A discovery phase before the main build, to turn your brief into a detailed, prioritised plan.
• Short delivery cycles, often called sprints, with working software you can see and test every couple of weeks.
• A named point of contact who understands both the technical and business sides.
• Source code in a repository you can access from the start, such as GitHub or Azure DevOps.
• Automated builds and deployments (often called CI/CD), so releases are repeatable rather than manual and error-prone.

Warning signs

• A fixed price for a large project before any discovery
• No demos until the end
• Vague answers about who will actually do the work

Want to see how automated delivery works? Read about our Azure DevOps consulting and wider DevOps consulting services.

5. Security and Quality Assurance

Security and testing are easy to promise and hard to check, so ask for specifics.

Security

Ask how the company:

• writes secure code, for example by following recognised guidance such as the OWASP Top 10 for web application risks
• keeps dependencies up to date, including .NET itself and third-party packages
• handles secrets such as passwords and API keys, for example using Azure Key Vault rather than storing them in code
• controls access to your systems and data
• handles personal data in line with UK GDPR

You can also ask whether the company holds Cyber Essentials, the UK Government-backed scheme for basic cyber security controls. It doesn't guarantee secure software, but it shows a baseline of organisational security. The NCSC's supply chain security guidance is also useful when assessing any supplier that will handle your systems or data.

Quality assurance

Good teams test throughout the project, not just at the end. Ask:

• Do you write automated tests, and which parts of the system do they cover?
• Who tests the software, and how?
• How do you handle user acceptance testing with our team?
• How do you check performance before launch?

6. .NET Development Costs in the UK

We haven't included general UK market prices here, because published rate surveys vary widely and quickly go out of date. Instead, focus on what drives cost and how to compare quotes fairly.

What affects the price

• Scope and complexity: the number of features, user roles and business rules.
• Integrations: each connection to another system adds design, development and testing work.
• Data migration: moving data from old systems can be a significant piece of work in its own right.
• Security and compliance: regulated sectors need extra controls and testing.
• Team location and seniority: UK-based, offshore and blended teams have very different day rates.
• Hosting and licences: Azure or other cloud costs, and any third-party licences, are usually separate from development fees.
• Support after launch: often charged monthly.

Common pricing models

How to compare quotes

Ask every company for an itemised quote that separates discovery, design, development, testing, project management, deployment and support, with VAT shown separately. Make sure each quote covers the same scope. A quote that's much cheaper than the others often leaves something out.

For context, see our software development cost guide and the rates on our hire .NET developers page.

7. Communication and Project Management

Many projects fail because of poor communication rather than poor code. Agree up front:

• Who your contact is, and who makes technical decisions.
• How often you'll meet, for example weekly progress calls and fortnightly demos.
• Which tools you'll use, such as Microsoft Teams, Jira or Azure Boards.
• Working hours, including overlap with UK hours if any of the team is based abroad.
• How changes are handled, including how they're priced and approved.
• How progress is reported, including budget spent against plan.

UK-based, offshore or blended teams

Whatever the model, insist on transparency about who does the work and where they're based. For more on this, see our guide to outsourcing custom software development.

8. Post-Launch Maintenance and Support

Launch is the start, not the end. Every .NET application needs ongoing care. Check that the company offers:

• Security and framework updates, including planned upgrades to new LTS versions of .NET.
• Monitoring of performance, errors and uptime.
• Bug fixes with agreed response times based on severity.
• Small enhancements as your needs change.
• Documentation and handover, so another team could take over if needed.

Make sure you own your software

Your contract should confirm that you own the source code, designs and documentation, and that your hosting, domains and cloud accounts are in your organisation's name. That way you're never locked in.

Supporting an older system? See our legacy application support and legacy app modernisation services. Moving systems to the cloud? See our cloud migration service.

9. A Scorecard for Comparing .NET Development Companies

Score each company from 1 (weak) to 5 (strong) on each criterion. Weight the criteria that matter most to your project.

10. Questions to Ask Before Hiring

1. Which .NET projects similar to ours have you delivered, and can we speak to a client?
2. Which version of .NET would you use, and how would you handle future upgrades?
3. Who exactly will work on our project, and where are they based?
4. How does your discovery phase work, and what will we receive at the end?
5. How often will we see working software?
6. How do you approach security, testing and UK GDPR?
7. How do you handle changes to scope, and how are they priced?
8. What's included in your quote, and what isn't?
9. Who owns the code, and how will we access it?
10. What support do you offer after launch, and what does it cost?

11. Common Mistakes to Avoid

• Choosing on price alone. The cheapest quote can become the most expensive if it leads to rework.
• Skipping discovery. Starting development without a clear plan almost always causes delays and extra cost.
• Ignoring the .NET version. Building on a version close to end of support creates an early upgrade bill.
• Not checking who does the work. Make sure the team you meet is the team that builds your software.
• No access to the code. You should be able to see your code from the first sprint.
• No plan for after launch. Agree support before development finishes.
• Vague contracts. Confirm scope, ownership, payment milestones and change control in writing.

12. Frequently Asked Questions