.NET Development in the UK

About .NET Development

We take on .NET builds as a senior engineering service: ASP.NET Core web apps and Web APIs, enterprise backends, and moving legacy .NET Framework code onto a modern, cross-platform stack. It is a newer service line for us, so we will say so plainly. You get senior engineers, a written scope, and a flat quote, and we lean on the API design, testing, CI, and migration work that carries straight over from the rest of what we build.

What the engagement includes

• You already run on Microsoft: SQL Server, Azure, Active Directory, or a team that standardizes on C#. .NET fits that estate with far less friction than bolting on a different runtime.
• You need a fast, strongly typed backend for high-throughput APIs. ASP.NET Core on Kestrel is genuinely quick, and static typing catches a whole class of bugs before they reach production.
• You are modernizing an old .NET Framework or WebForms app and want to stay in the same language and hiring pool instead of rewriting in something unfamiliar to your team.
• Your team hires C# developers and will own the code after us. Handing a Node or Laravel app to a .NET team, or the reverse, is a real long-term cost worth avoiding.
• If none of that is true and you are starting fresh with no Microsoft ties, we will often steer you to Node or Laravel instead, the stacks we run deepest in. Saying that costs us the .NET brief and saves you money, which is the trade we would rather make.

MTD for Income Tax, payrolled benefits from April 2027 and the golden thread in a UK .NET system

Making Tax Digital for Income Tax went live on 6 April 2026 for sole traders and landlords whose qualifying income, their self-employment and property turnover before expenses, was over £50,000 on the 2024 to 2025 return, and HMRC's guidance lines up £30,000 from 6 April 2027 and £20,000 from 6 April 2028. For a .NET accounting or lettings product, what differs from the VAT version is the shape of the obligation. A quarterly update is not three months of figures: each one runs from the start of the tax year to the end of the update period, so the second update of 2026 to 2027, due by 7 November 2026, is cumulative and quietly corrects whatever was wrong in the first. The software therefore stores the categorised totals it actually sent, not a flag saying sent, and recomputes the year to date from the digital records each time. Update periods come in two kinds, standard ones ending on the 5th to match the tax year and calendar ones ending on the last day of the month for accounts running from 1 April, and HMRC's developer newsletter of 30 September 2026 warns that switching type and submitting before the change shows in the software lands updates on the wrong period, and that the type cannot change once the year's first update has gone. The same newsletter lists retirements: version 2 of the capital gains and reliefs APIs goes on 16 October 2026, and returns for 2026 to 2027 should use version 7 of the losses API. In a .NET client those versions belong in configuration, with a typed HttpClient per API sending its version in the Accept header, so a retirement is a settings change and a test run. HMRC is not applying penalty points to late quarterly updates in 2026 to 2027, which makes this the cheap year to find the gaps. Whether a user must sign up, and from when, is for their accountant.

Payroll products have a fixed date too. HMRC's policy paper of 13 July 2026 makes payrolling mandatory from April 2027 for company cars, car fuel, vans, van fuel and employer-provided medical benefits, with most other benefits following in April 2028 and loans and accommodation to be confirmed later. The year-end P11D gives way to fields on the Full Payment Submission, and the interim guidance, updated on 23 September 2026, lists the likely ones for cars: make and model, date first registered, CO2 emissions, zero emission mileage, fuel type, a car identifier, the dates the car was available from and to, and the cash equivalent for the pay period and the year to date, with matching totals for vans, fuel and medical cover and new fields for Class 1A National Insurance paid in real time. Technical specifications are promised for this autumn, so in a .NET payroll engine the fields arrive as a versioned schema change behind the FPS builder rather than edits to classes already in use. The logic is where it bites. Tax deducted in a period cannot exceed half of that period's pay, the overriding limit, so the excess carries forward and whatever is still uncollected at year end is left for HMRC, which means the engine holds an uncollected balance per employee rather than letting the calculation fail. A director paid no cash earnings still needs an FPS reporting the benefit, and so does a leaver who keeps the company car. Employers who want to payroll other benefits voluntarily register through a service opening in November 2026, with 5 April 2027 as the deadline. HMRC says inaccuracies in 2027 to 2028 returns linked to the change will not be penalised unless deliberate, though late filing penalties still apply. How each benefit is valued and taxed is for your accountant.

Software holding building records in England has a statutory standard to meet since the Building Safety Act 2022 created the golden thread for higher-risk buildings: at least 18 metres or seven storeys high with at least two homes. Regulation 7 of the Higher-Risk Buildings (Management of Safety Risks etc) (England) Regulations 2023 sets out how the information is kept, and it reads like a requirements list for a document system. It must be in an electronic format that can be transferred to someone else without the data being lost or corrupted, accurate, intelligible to its readers with any key needed to understand it supplied alongside, accessible as soon as reasonably practicable when an entitled person asks, secure from unauthorised access, and changed only through procedures that record who made each change and when. On a .NET and SQL Server stack that last point maps onto system-versioned temporal tables, which Entity Framework Core has supported since version 6, so the history is kept by the database rather than by application code someone can route around, with the authenticated user written on every row because the table records when but not who. Transferability is the requirement buyers miss. Accountable persons change when a building is sold or its management moves, and an export the next owner cannot open fails the standard, so the data leaves in open formats, documents in their original files, with a readable index, and the export is tested by importing it somewhere else. The same regulations require one mandatory occurrence reporting system per building, open to all residents and users, with a safety occurrence notified to the Building Safety Regulator as soon as reasonably practicable and a full report within 10 days of it coming to the accountable person's attention, so a resident's report starts a clock the system has to show. Whether a building is in scope is for your building safety adviser.

How we work with UK clients

UK engagements tend to start with procurement questions rather than technical ones. Who holds the data, which law governs the contract, whether you can produce a record of processing if the ICO asks. We answer those in the proposal instead of leaving them to a legal review three weeks in, because that review is where UK projects usually stall.

Invoicing is the other thing worth settling early. We are outside the UK, so services we supply generally fall under the reverse charge and your finance team accounts for the VAT rather than paying it to us. Our invoices say so explicitly. We quote in pounds, the figure does not move with the exchange rate mid-project, and payment by bank transfer avoids the card fees that make a five-figure invoice unnecessarily expensive.

Questions UK clients ask

.NET Development: common questions

Other markets we work in