How to hire an AI agent developer in the UK
Most of the search results for "hire an AI agent developer" are marketplaces and offshore agencies quoting US dollar rates. This guide is for UK organisations. It covers what the job involves, when you actually need someone, what to ask, how engagements are usually set up, and what the published rate data says about cost.
I'm Tony James, an applied AI and full-stack engineer based in Milton Keynes, so I have an interest here. I've tried to write the guide I'd want to read if I were the one hiring.
What an AI agent developer actually does
An AI agent is software that uses a language model to decide what to do next, then does it by calling tools: your APIs, a database, a calendar, a ticketing system. A chatbot answers questions. An agent takes actions.
The developer's job is mostly ordinary engineering around the model:
- Tool use. Wiring the agent to your systems through well-defined functions, with structured outputs that your code can check. - Retrieval (RAG). Giving the agent the right documents and records at the right moment, so it answers from your knowledge rather than guessing. - Guardrails. Limits on what the agent may do, when a human must approve, and what happens when the model is wrong. - Testing and evaluation. Repeatable checks that show whether a change made the agent better or worse. - Deployment and running costs. Logging, monitoring and keeping an eye on model usage once real users arrive.
If a candidate talks mainly about prompts and demos, and rarely about integration, testing and failure handling, they are describing a prototype, not a production system.
When you need one, and when you don't
You probably don't need a developer if a packaged product already does the job. Plenty of support-chat, meeting-notes and email tools now include agent features. Buy those first.
You probably do need one when:
- the agent has to act inside your own systems (CRM, ERP, internal APIs), not just answer questions; - the knowledge it needs is spread across your documents and databases; - you need to own the code, control where data goes, or meet a compliance requirement a SaaS vendor can't; - a pilot works in a demo but falls over with real data and real users.
Typical engagement shapes
UK engagements tend to take one of four forms:
1. Discovery or spike. A short, fixed piece of work to test one workflow with your real data and say honestly whether an agent is the right tool. 2. Fixed-scope build. One agreed agent or workflow, delivered with tests, documentation and a handover. 3. Embedded contract. A contractor works inside your team on a day rate, usually through a limited company or an agency. 4. Ongoing support. A smaller retained arrangement for monitoring, model upgrades and improvements after launch.
If you engage a contractor who works through their own limited company, check the off-payroll working rules (IR35). HMRC's guidance says that in most cases the client decides the worker's employment status for tax, and should produce a status determination statement. If the client is a small business outside the public sector, the contractor's own company makes that decision instead. A fixed-scope deliverable from a business supplier is set up differently from an open-ended day-rate role, so take advice if you're unsure.
What to ask before you hire
- What have you shipped that is still running, and who used it? Ask for production work, not demos. Ask what broke after launch. - How will you test it? You want a concrete answer about evaluation sets, regression checks and how "good enough" is measured. - What can the agent do without a human? A good developer will push for narrow permissions and approval steps on anything costly or irreversible. - Where does our data go? Which model providers, which regions, what is logged and for how long. If personal data is involved, the ICO's guidance on AI and data protection expects you to think about accountability and, often, a data protection impact assessment (DPIA). Your developer should be comfortable with that conversation. - Who owns the code and prompts? Make sure the contract assigns IP to you and that the work lives in your repositories. - What will it cost to run? Model usage, hosting and monitoring are ongoing costs, separate from the build. - How do we switch models later? Providers change prices and models often. Ask how much of the system depends on one vendor.
Red flags
- Guaranteed accuracy figures before they have seen your data. - No mention of testing, logging or human approval. - "Fully autonomous" pitched as a feature rather than a risk to manage. - Work kept in their accounts, not yours. - A large upfront build with no small first milestone. - Case studies with no named outcome you can check, or results borrowed from a vendor's marketing.
What it costs
There's no standard price for "an AI agent", but there is some public data.
Contract day rates. IT Jobs Watch tracks UK contract vacancies. For the six months to 6 October 2026, it recorded 841 contract jobs citing AI Agents, 540 of which quoted a daily rate. The median was £575 a day. The 10th percentile was £424 and the 90th was £851. The median outside London was £525. These are advertised rates in job ads, not quotes from individual freelancers, but they give you a fair benchmark for embedded contract work.
Project ranges from agencies. Some UK agencies publish indicative build ranges. LeverX, for example, suggests about £10,000–£30,000 for a single-workflow agent and £30,000–£80,000 for a multi-step agent with integrations. Fulminous gives £8,000–£25,000 (ex VAT) for a simple single-task agent. Treat these as one supplier's view of the market, not a price list.
Running costs. Fulminous also notes that model usage alone can run from about £150 to over £5,000 a month depending on volume and model. Ask any supplier to estimate this for your expected volumes.
By Tony James