ON3 Works is an IT recruitment agency covering the whole UK. AI screens to a qualified shortlist in 24 to 48 hours; on the Atelier tier a senior engineer in the same stack interviews every finalist before you see them. Fees are 7% (Agentic) or 20% (Atelier) of first-year salary, success fee only, no deposit, free replacement inside 90 days: on a £100,000 senior backend hire, £7,000 or £20,000 against £18,000–£22,000 from a typical agency. You hire the engineer directly; ON3 finds and vets them.
What hiring engineers in the UK looks like in 2026
The UK is Europe's deepest engineering market and its most expensive. Demand is concentrated in AI/ML, data, cloud and DevOps, and payments infrastructure, and pay reflects scarcity: a backend engineer in London sits around £75,000 at the mid-point of the market, senior profiles near £95,000 and the top decile above £125,000 in cash, from ON3's index of 1.7M+ UK and Spanish technical profiles. London is the largest single market, but a third of our UK placements sit outside it: Manchester, Edinburgh, and remote or hybrid roles nationwide.
Speed is the other pressure. The UK average time to hire is about 4.9 weeks, and specialist tech roles often run 6 to 8 weeks in-house [StandOut CV; NatWest Mentor, 2026]. The strongest engineers are off the market within days, which is where in-house searches lose them. ON3 is built for that gap: a qualified shortlist in 24 to 48 hours and a median hire in under 30 days, the same speed in every UK region.
Before opening a search, decide how to run it at all. We set out the real numbers on using an agency versus hiring in-house, cost per hire, time to fill and bad-hire risk, and on how an AI-led process compares to a traditional agency.
UK engineering pay, from ON3's dataset
Indicative annual base salary by role and seniority, drawn from ON3's UK profile index. Useful for setting a realistic offer before you open a search.
| Role (London) | Junior | Mid | Senior |
|---|---|---|---|
| Backend engineer | £31k–48k | £64k–101k | £79k–121k |
| Full-stack engineer | £32k–45k | £45k–75k | £70k–100k |
| ML / AI engineer | £38k–54k | £52k–95k | £86k–142k |
| DevOps / platform engineer | £26k–40k | £50k–80k | £69k–102k |
Source: ON3 Works index of 1.7M+ UK and Spanish technical profiles, refreshed daily (2026). Figures are indicative base salary; London-weighted. Independent aggregators put London backend in a similar range (Glassdoor median ~£79k, 90th percentile ~£128k).
The fee on each role, at UK rates and at ON3's
UK IT recruitment agencies charge 18% to 22% of first-year salary on contingency, 22–25% for ML and security, and 25% to 33% for a retained search with a third paid before you see a CV. ON3's two tiers are success fees with no deposit: 7% for the AI-led search and 20% when a senior engineer interviews every finalist.
On a mid-level full-stack engineer at £60,000 the gap is £10,800–£13,200 against £4,200; on a senior ML engineer at £114,000, £25,100–£28,500 against £8,000 or £22,800. How UK fees are built, the clauses that change the invoice and what temp and contract agencies charge per hour are in our guide to recruitment agency fees UK; the recruitment fee calculator runs the maths on any salary, with VAT and the rebate schedule.
| Role · London mid-point | Salary | UK agency (18–25%) | ON3 Agentic 7% | ON3 Atelier 20% |
|---|---|---|---|---|
| Mid backend engineer | £82,500 | £14,850–£18,150 | £5,800 | £16,500 |
| Senior backend engineer | £100,000 | £18,000–£22,000 | £7,000 | £20,000 |
| Mid full-stack engineer | £60,000 | £10,800–£13,200 | £4,200 | £12,000 |
| Senior full-stack engineer | £85,000 | £15,300–£18,700 | £5,950 | £17,000 |
| Mid ML / AI engineer | £73,500 | £16,150–£18,400 | £5,150 | £14,700 |
| Senior ML / AI engineer | £114,000 | £25,100–£28,500 | £8,000 | £22,800 |
| Mid DevOps / platform engineer | £65,000 | £11,700–£14,300 | £4,550 | £13,000 |
| Senior DevOps / platform engineer | £85,500 | £15,400–£18,800 | £6,000 | £17,100 |
Salary is the mid-point of the London band for that role and level; agency percentages are the typical UK ranges for tech (18–22%, ML and security 22–25%). All fees exclude VAT. Your quote may differ.
Six questions that separate IT recruitment agencies
1 · Who evaluates the candidate? A keyword match is not a technical screen. Ask whether an engineer who has worked in the stack speaks to the candidate before you do, and what you receive: a CV, or an assessment of how they code, design and reason. At ON3 the Atelier tier means a senior engineer with 8 to 15+ years in that stack interviews every finalist.
2 · Where do candidates come from? The agencies worth paying find the engineers who are not applying. Ask what share of recent placements were passive candidates and how they were sourced, not just how big the database is.
3 · What is the fee model, and what triggers it? Contingency, retained or success-only; base salary or total package; what happens if you hire someone they introduced twelve months later. Our fees guide walks through the six clauses in a terms of business that change the bill.
4 · What happens if the hire leaves? A sliding rebate over 8 to 12 weeks is the UK norm, often conditional on paying the invoice on time. A free replacement is the stronger guarantee; ON3 gives 90 days.
5 · How fast is the first shortlist, and how fast is the hire? Days, not weeks, for the shortlist; ask for the median time from brief to accepted offer and for the retention rate at twelve months. ON3's are under 30 days and 90.7%.
6 · Can they hire the role somewhere cheaper? If the London band does not fit the budget, an agency that only recruits in the UK cannot help. The next section is why UK employers come to ON3 for exactly that.
The same role from Madrid or Barcelona, through the same team
ON3 recruits in the UK and Spain from one office, so we see both price lists. Senior engineers in Spain who spoke to us in 2025–26 asked for a median of €50,000 a year (the 90th percentile is €75,000); a senior with C1 English asks about 21% more than one with B1. Against a London senior backend band of £79k–121k, that is roughly half the cash cost for the same seniority, before employer contributions on either side. [ON3 Works, tech salary expectations in Spain 2026, 3,389 candidates]
The world's largest technology companies already hire this way: of the 238 Spain adverts we coded from the 250 most valuable tech companies, 54 are fully remote roles and 36 are open across several countries at once. The practical route for a UK company is an employer of record or a Spanish entity, English-first teams and a one-hour time difference. The per-role comparison, London band against Spanish scale-up and international hub, is on the London page; the data behind it is in tech salary expectations in Spain and big tech hiring engineers in Spain.
Two tiers, one engineer-led standard
Both tiers run on the same UK-wide sourcing and the same engineer-led quality bar. A precise note on the 24 to 48 hours: that shortlist is AI-screened and qualified, not yet engineer-interviewed. In Atelier, the senior-engineer interview follows before any candidate reaches you. No deposit, billed in GBP, with a free replacement inside 90 days. Full tier detail is on the pricing page.
Software, data, cloud, cybersecurity and deep tech
ON3 built its reputation in software and is growing fast in cybersecurity and deep tech, including chips and HPC, a particular UK strength. Each role type is broken down in the profiles we cover directory. Common UK searches:
- Backend
- Full-stack
- Frontend / React
- ML / AI
- Data engineering
- Platform
- DevOps / cloud
- Cybersecurity
- Engineering leadership / CTO
Who ON3 hires for in the UK
Two kinds of buyer. Teams tired of traditional agencies charging a fortune for work they could do themselves come to ON3 for rigorous technical vetting: profiles that are fully checked and actually fit the brief. And teams under urgent pressure, who never used agencies because of cost, try the Agentic model at 7%. In the UK specifically, quality tends to weigh even heavier than speed.
One example: a YC-2023 company that raised a Series B in 2026 used ON3 to hire 12 technical staff, working through ON3's venture-capital channel to find qualified candidates fast. CGI, the global consultancy, uses ON3 for 50+ hires a year and operates in the UK as well as Spain.
“ON3 Works has become my favourite external recruiting partner. They're fast, efficient, and bring us candidates already vetted, qualified, and ready to hire. They've made talent search easy for me and my team.”
— Gabriel Garcia, Vice-President Consulting Services, CGI
IT recruitment agencies in the UK: frequently asked questions
What does an IT recruitment agency do?+
How much do IT recruitment agencies charge in the UK?+
How long does it take an IT recruitment agency to fill a role?+
What is the difference between an IT recruitment agency and an IT staffing agency?+
Do you cover roles outside London?+
Can a UK company hire engineers in Spain through ON3?+
Which engineers do you recruit?+
Are ON3 a recruitment agency or do you employ the engineers?+
Tell us who you need to hire
Send us the role. You'll get a qualified shortlist in 24 to 48 hours and a fee quote on both tiers; for critical hires, a senior engineer who interviews every finalist.
Tell us who you need to hire →- GUIDE · Recruitment agency fees UK: how much do agencies charge?
- TOOL · Recruitment fee calculator
- LOCATION · Tech recruitment agency in London
- COMPARE · Recruitment agency vs in-house hiring
- COMPARE · AI recruiting vs a traditional agency
- COMPARE · Toptal alternative for permanent hiring in Europe
- STUDY · Tech salary expectations in Spain
Sources & notes
ON3 figures Salary bands from the ON3 index of 1.7M+ UK and Spanish technical profiles (2026); 7%/20%, no deposit; 24 to 48h shortlist; <30-day median hire; 90.7% retention; 90-day replacement; about two thirds of UK placements London-based; YC/Series-B and CGI references: supplied by ON3 Works.
Agency fees 15–25% contingency across all roles, 18–22% for tech, 22–25% for ML and security, 25–33% retained: typical UK published rates (Recruitly 2026, Leonar 2026) and ON3 client data. Contract markups 12–18% on the day rate. Fee examples use the London band mid-points; VAT excluded.
Spain ON3 Works, tech salary expectations in Spain 2026 (3,389 candidates, 2025–26): senior median ask, 90th percentile and the C1-English premium. ON3 Works, big tech hiring in Spain (14 October 2026): remote and multi-country adverts.
UK time to hire ~4.9 weeks all roles; tech 6 to 8 weeks: StandOut CV; NatWest Mentor (2026). Independent salary cross-check (London backend ~£79k median, ~£128k 90th percentile): Glassdoor; IT Jobs Watch (2026).
Note The 24 to 48h shortlist is AI-screened and qualified, not yet engineer-interviewed; the engineer interview follows in Atelier. Salary figures are indicative and should be confirmed for a specific role and location.