Mobile app development in London
For a London challenger bank or payments app, the app is the product and its reviews are public. Biometric sign-in, device binding and step-up checks for risky payments all live on the phone, and each one is a place where a sensible security rule can turn into a customer who cannot pay for their lunch. The work is getting both right at once.
We build in React Native, one codebase for iOS and Android, with the security-sensitive pieces done natively where they need to be. We treat the API contract as part of the app, because most mobile bugs in fintech are really backend timing bugs. Amour, our own app, taught us the value of review and moderation running behind the user rather than in front of them, and the same pattern applies to fraud checks.
Financial services drive more of London's software demand than any other sector. Payments companies, challenger banks, wealth platforms and brokers need ledgers that reconcile, APIs that stay correct when a partner retries, and apps customers trust with their money. Most of them reached the market fast, which was the right call at the time, and now run systems built for launch rather than for the size they have become. The work is making those systems dependable without stopping the business that runs on them.
Insurance is its own case. The specialty insurers, managing agents and brokers around Lloyd's still run much of their work on ageing policy administration platforms and spreadsheets that travel between firms by email. Lloyd's has moved away from Blueprint Two, the market-wide programme that was meant to digitise placement and claims, so each firm is modernising its own systems one integration at a time. The City's law firms and consultancies sit alongside them, holding decades of documents and few ways to search them by meaning.
Media, retail and the public sector bring different problems. Publishers run subscriptions, paywalls and content systems that have to hold up on a busy news day. Direct-to-consumer brands outgrow their first shop as they start selling into Europe and the US. Suppliers to councils and NHS bodies build services that have to work for every resident, including people using a keyboard or a screen reader. Hiring is the common constraint. ITJobsWatch puts the median advertised salary for a software engineer in London at £98,750 over the six months to September 2026, and banks, fintechs and the large technology firms compete for the same people.
Working with us from London is straightforward. Four hours of every working day overlap with yours, set across your morning, so stand-up, code review and the decisions that follow happen live. You talk to the engineer who writes the code, in your own Slack, GitHub and Linear. The rest of the day moves forward in pull requests you can read at your desk, with runbooks and architecture notes written as the work goes.
We are the right fit when you have a defined piece of work and need senior engineers on it this month rather than next quarter. Start with a fixed-price two-week piece and judge us on what ships. We add capacity while a London hire is still in progress, and we work white-label under your name for agencies.
Four ways this arrives.
And crashes on the ones your users own. We add crash reporting with readable stack traces, find the handful of devices and OS versions causing most of the crashes, and fix those before anyone touches a feature.
Signing keys on a laptop, a manual build, store notes written at midnight. We move builds and signing into CI, add over-the-air updates for JavaScript-only fixes, and write down exactly how a release goes out.
A Bluetooth device, a vendor SDK, a camera pipeline, a background task the OS keeps killing. We write the native module in Swift and Kotlin, expose a small typed interface to React Native, and keep it isolated so upgrades stay possible.
Forms that vanish, actions that send twice. We decide what must work offline, keep it on the device, queue writes with idempotency keys the backend understands, and show the user plainly what is still waiting to sync.
Our own React Native app on Android, with retraction built into the client because moderation can pull a message after it has been sent.
Read the write-up →Asked by London teams.
How do you work with teams in London?+
Four hours of every working day overlap with yours, set across your London morning, so stand-up and code review happen live. We join your calls and work in your tools: Slack, GitHub and Linear. You talk directly to the engineer who writes the code. Outside the overlap, the work carries on in pull requests you can read at your desk, and runbooks and architecture notes are written as we go.
Do you build for London fintechs and insurers?+
Yes. For payments companies, challenger banks and wealth platforms we build ledgers that reconcile, webhook handling that stays correct when a provider retries, and React Native apps with biometric sign-in and step-up checks for risky payments. For insurers, managing agents and brokers around Lloyd's we replace spreadsheet workflows with internal tools: bordereaux intake, referral queues and approvals, connected to the policy systems you already run.
How does your rate compare to hiring in London?+
ITJobsWatch puts the median advertised salary for a software engineer in London at roughly £99,000. Our published rate is $35/hour, with a $5,000 minimum engagement. There is no recruiting time and no employment overhead, and we can start within days of the first call. Most clients begin with a fixed-price two-week piece at $2,800, so you judge us on working code before committing to more.
Can you work white-label for a London agency?+
Yes. London agencies bring us in when a client project needs more senior backend, mobile or infrastructure work than the team has free. We work under your name, in your repositories and your client's tools, and you stay the face of the project. The NDA comes before specifics, the code belongs to the client from the first commit, and runbooks and architecture notes are written as we go.
React Native or fully native?+
React Native for most products: one codebase, one team, both stores. Fully native makes sense when the app is mostly the hard native part, such as heavy camera or audio processing, complex background work, or a platform feature React Native does not support yet. We will tell you which side of that line you are on, and write the native parts by hand either way.
Expo or bare React Native?+
Expo, in almost every case now. Development builds and config plugins removed most of the old reasons to eject, and EAS handles builds and signing. We go bare only when a native dependency genuinely cannot live inside a config plugin, and we will explain why before doing it, because it makes every future upgrade more work.
Can you take over an app someone else built?+
Yes. We start by getting it to build on a clean machine, which is often the hardest step, then bring React Native and its dependencies up to a supported version before adding features. We tell you what state the app is in, including where the store listings, signing keys and accounts actually live, before quoting anything larger.
Who handles App Store and Play Store submission?+
We do, from your developer accounts, not ours. We prepare the builds, the privacy disclosures and the notes for the reviewer, and deal with rejections when they come. The accounts, signing keys and listings stay in your name, so you can change developers later without asking anyone's permission.
Does our backend need to change for a mobile app?+
Often, a little. A mobile client stays on old versions for months, retries on bad networks, and cannot be fixed by a server deploy. That means versioned endpoints, idempotent writes, and a way to tell an old client it must update. We check the backend for those before the first screen is built, because retrofitting them after launch is slower.