How to Find Reliable Subcontractors and Vet Them
The short answer
Find reliable subcontractors through referrals from trades you already rate, then vet every one before the first job: see finished work, call two past clients, check insurance and CIS status, agree terms in writing and give them a small trial job before a big one.
- Referrals beat adverts. Your best subbies know other good trades. Ask them first.
- See the work, call the clients. Photos are easy to borrow; a past client on the phone is not.
- Paper before the first day. Insurance on file, CIS verified with HMRC, scope and payment terms in writing.
- Small job first. Try a new subbie on a small job before you trust them with a £100K extension.
A bad subbie costs more than his invoice. He walks off halfway through, leaves work you have to rip out, and the programme slips on every job behind him. Most builders find subcontractors the same way: a mate's number, a Facebook group, a price that sounded right.
This guide shows how to find reliable subcontractors and vet them before the first job. It is for owners of UK building companies who rely on trades they do not employ. It is the selection step that comes before managing subcontractors. Want a supply chain you can grow on? Book a free strategy call.
Why one good subbie per trade is not enough
If one electrician lets you down and the whole programme stops, you do not have a supply chain. You have a single point of failure.
Aim for two or three reliable subbies per trade you use most: electrics, plumbing, plastering, decorating, tiling, joinery, groundworks. Then one holiday, one illness or one better-paying job elsewhere does not stop your sites.
That means you are always finding and testing new trades, even when you are busy. The best time to find a plasterer is before you need one on Monday.
Where to find reliable subcontractors
Start where the trust is already earned, and work outwards:
- Your best subbies. Good trades know other good trades. Ask your electrician which plumber he would work with again.
- Merchants and suppliers. The counter staff know who pays, who orders properly and who turns up every week.
- Other contractors you trust. Builders who do different work in your area often share trades.
- Your own sites. Note the trades on neighbouring jobs who work tidily and finish on time.
- Trade groups and platforms. Fine for volume, but vet these hardest. A profile is not a reference.
Short of your own employees too? See how to find good tradesmen to hire.
How to vet a subcontractor before the first job
Vetting takes an hour. Fixing a bad job takes weeks. Before a new subbie starts, check:
- finished work: photos plus an address you could visit
- two references: past clients or contractors, called by you
- public liability insurance: a copy, in date, on file (if a sub damages next door, see damaged a neighbour's property during building work)
- CIS status: verified with HMRC before the first payment
- who turns up: the person who prices is the person who works
Photos are easy to borrow from someone else's job. A past client on the phone is not. Ask them three things: did he finish on time, was the price the price, and would you use him again?
Taking a subbie on because he was the only one free this week. Desperation is how most bad subbies get onto good jobs.
Verify them for CIS before you pay
If you are a CIS contractor, you must verify a new subcontractor with HMRC before you pay them. Use HMRC's free CIS online service or CIS software. You need:
| From you | From the subbie |
|---|---|
| Your UTR | Their UTR |
| Accounts office reference | Sole trader: National Insurance number |
| Employer reference | Limited company: name, company UTR and registration number |
The details must match exactly how they registered with HMRC. Temporary NI numbers starting "TN" cannot be verified. HMRC then tells you the rate: 20% if they are registered, 30% if not, or nothing if they hold gross payment status.
Check the working arrangement too. If someone works only for you, on your hours, with your tools, HMRC may treat them as your employee. Re-verify any subbie who has not been on your CIS return in the current or last two tax years.
Agree payment terms and paper before day one
Every argument at the end of a job started with something never written down. Before a new subbie starts, agree in writing:
| Item | What to agree | Why it protects you |
|---|---|---|
| Scope | Drawings and a written list of what is included | They price the real job, not a guess |
| Price | Lump sum, day rate or measured rate | No "that was extra" at the end |
| Materials | Who supplies what | No double orders, no missing items |
| Payment | How they apply, when you pay, any retention | They know when money arrives; you control cash |
| Variations | Only on a signed form, priced before the work | You never pay for extras you cannot bill |
| Non-solicitation | They do not approach your client directly | Your client stays your client |
A one-page subcontract order covers most small jobs. Have a solicitor check your template once, then use it every time. For the client-poaching risk, see non-solicitation agreements in construction.
Not sure your subcontract paperwork protects you?
Book a free strategy call and we will go through it with you.
The trial-job rule and the red flags
Try every new subbie on a small job before you trust them with a £100K extension. A bathroom, a single room, one day of snagging. Watch three things: did they start when they said, was the finish right first time, and did they send a daily photo when you asked?
Walk away, or slow down, when you see these red flags:
- Cash upfront for labour. Pay the merchant for materials yourself; pay labour against work done.
- No paperwork. No UTR, no insurance copy, "we'll sort the contract later".
- A price far below the others. Either the scope is missed or the job will be.
- Someone else turns up. The man who priced it sends a crew you have never met.
- Bad-mouthing every past contractor. You will be next on that list.
After the trial, score them: quality, speed, tidiness, communication. Give the next job to the best score, and pay on time, every time. The best subbies choose who they work for.
For a four-minute score of your systems, cash, sales and pricing, take the free Construction Business Scorecard.
What a working supply chain makes possible
What this looks like in practice. Adam and Ali grew their building company by subcontracting the delivery of their £49K and £12K jobs, while Adam moved to sales. Subcontracting works when the system around it does. Individual results, not typical or guaranteed.
Sviat Jay runs Craftex, a London design and build company that delivers its projects through a supply chain of trades. He mentors owners one to one himself. Some owners are strong on site and weak on paper; others have the paperwork but no bench of trades. He works on your weak spot first.
He is aiming for results in about 4 months rather than 1–3-year programs. Already let down mid-job? See subcontractor walked off the job. To build your supply chain with us, book a free strategy call.
Want a bench of subbies you can trust on every job?
Book a free strategy call.
Before your next new subbie starts
Tax points are general information as of October 2026. Check the details with your accountant.
Before you go
- You have seen finished work and called two past clients
- Insurance is on file and CIS is verified with HMRC
- Scope, price, payment and variations are agreed in writing
- Their first job with you is a small one
- You will score them after the job and pay them on time
