How to Go From Subcontractor to Main Contractor
The short answer
Becoming a main contractor means taking the client contract and responsibility for every trade. In the UK that means registering as a CIS contractor, meeting CDM principal contractor duties, carrying the right insurance and accreditations, using proper contracts and funding the gap between paying subbies and getting paid.
- You take on the risk of every trade. The client contracts with you. Programme, quality, safety and payment to subbies become your problem.
- CIS flips. You register as a contractor, verify every subbie, deduct 20% (30% if unverified) and file a return by the 19th of every month. A late return starts at £100.
- CDM duties arrive. On any job with more than one contractor, the principal contractor writes the construction phase plan, runs inductions and provides welfare from day one.
- Cash is the real test. You pay subbies before the client pays you, and retentions are typically 5%. Agree stage payments and payment dates in the contract.
Most subcontractors who want to become a main contractor already have the skill. What changes is the job description. You stop delivering one trade and start answering for all of them: to the client, to HMRC and to the HSE.
This guide is the UK route, step by step. It covers what the law asks of you, what clients will check, how the money works and who you need around you. Want the move planned around your trade? Book a free strategy call.
If you are not sure of the basic difference, start with contractor vs subcontractor. Still building volume as a subcontractor first? See how to get subcontract work from main contractors.
What actually changes when you become the main contractor
As a subcontractor, someone else holds the risk. As a main contractor, you do.
| Subcontractor | Main contractor | |
|---|---|---|
| Contract with | The main contractor | The client |
| Responsible for | Your trade or package | The whole job: programme, quality, safety, handover |
| CIS | Has deductions taken | Registers, verifies subbies, deducts, files monthly |
| CDM (more than one contractor) | Follows the site rules | Usually the principal contractor: plans and controls the site |
| Cash | Waits for the main contractor | Pays subbies, waits for the client |
| Margin | On your labour | On the whole job, plus management |
The upside is the margin on the whole job and direct contact with the client, the architect and the next project.
Step 1: Get the legal set-up right
Three sets of rules change the day you take on a whole job.
CIS: you become the contractor
- Register with HMRC before you take on your first subcontractor.
- Verify every subcontractor with HMRC before you pay them.
- Deduct 20% from the labour part of each payment (30% if they are not registered), unless they hold gross payment status.
- File a monthly return by the 19th. Late returns cost £100 at one day, £200 at two months, then £300 or 5% of the deductions.
- Check employment status. If a "subbie" works only for you, on your hours, with your tools, HMRC may say they are an employee.
CDM 2015: you may be the principal contractor
On any project with more than one contractor, the client appoints a principal contractor to control the construction phase. That is usually you. You must:
- Write a construction phase plan before work starts
- Plan, manage, monitor and coordinate the whole construction phase
- Give every worker a site-specific induction
- Provide welfare facilities from the first day
Your company structure. Sole traders, partnerships and limited companies can all be CIS contractors. A sole trader is personally responsible for all the business's debts. Most owners taking on whole jobs move to a limited company. See how to structure a construction company.
Paying a new subbie before verifying them with HMRC. You cannot know the right deduction rate, and errors land on your return.
Winning commercial work is a sales system, not luck. Take the free 4-minute Construction Business Scorecard: 18 questions on your pipeline, sales, pricing, cash flow and systems, with your weakest area shown first. Short of time to write bids? See our bid writing service.
Step 2: Insurance and accreditations clients check
Before a bigger client sends you drawings, they check your paperwork.
- Employers' liability: the law. Required once you employ anyone (family-only firms are exempt), with at least £5 million of cover. The fine is £2,500 for every day without it.
- Public liability and contract works: the contract. Not required by law, but most clients and main contracts ask for them, with a set level of cover.
- Professional indemnity: if you design. Moving into design and build? Ask your broker, and read how to become a design and build company.
- Health and safety accreditation (SSIP). CHAS, SafeContractor or SMAS are the common entry level for private commercial clients.
- Build UK Common Assessment Standard. One yearly assessment accepted by Balfour Beatty, HS2, Kier, Mace and Wates. Public sector buyers are told to use it. CHAS, Constructionline and SMAS are among the bodies that certify it. How it fits into public work: how to get on construction frameworks and how to win council contracts.
- ISO 9001, 14001, 45001. Asked for on larger commercial and public tenders.
Craftex, the main contractor Sviat Jay runs, holds CHAS, SafeContractor and ISO 9001, 14001 and 45001. Get only what your next target client actually asks for. Accreditation is a cost until it wins you a job.
Not sure which accreditations your next client will ask for?
Book a free call and we'll check against the work you want.
Step 3: Use contracts that protect you
As a subcontractor you sign what you are given. As a main contractor you write it, so get it right.
- One standard form, two directions. A recognised form (JCT or NEC) with the client, and back-to-back subcontracts with your trades so the same terms flow down.
- Stage payments and dates. Deposit, stages tied to work done, and a payment date for each.
- Written variations. Nothing extra starts without a price and a written yes.
- Retention. Typically 5%, half at completion and half after a defects period that is usually 12 months. Negotiate it down or agree a retention bond.
Know your rights in law. "Pay when paid" clauses do not work unless the payer is insolvent. If a sum is not paid on time, you can suspend work after giving at least seven days' notice.
Match your terms down the chain. If the client pays at 30 days and you promised your trades 14, you are funding the job.
Step 4: Fund the cash-flow gap
This is where most first main contracts go wrong. The work is fine. The bank balance is not.
Example figures (not a real job): a £40,000 refurbishment over 8 weeks. You pay subbies and materials about £28,000 as the job runs. The client pays monthly against valuations, 30 days after each one. In week 6 you may have paid out most of the £28,000 and received one payment. At the end, 5% retention (£2,000) stays with the client.
How to close the gap:
- Deposit before you order materials.
- Stage payments small and frequent enough to stay ahead of your costs.
- Supplier credit agreed before the job, not during it.
- VAT: when VAT-registered subbies invoice you under CIS, the domestic reverse charge usually applies. Check with your accountant how it works on each contract.
- Gross payment status for your own firm. It stops 20% being taken from your labour when you still work as a subbie. The turnover test for a company is £30,000 per director or £100,000 overall, excluding VAT and materials. If HMRC has refused or removed it, see CIS gross payment status refused or removed.
Step 5: Build the team and the subbie bank
You cannot run three jobs from the tools. The roles you need, roughly in order:
- Site lead. Runs each job day to day so you are not needed on site.
- Two or three subbies per trade. Rates, terms and quality standards agreed in writing. Pay on time, every time.
- Admin. CIS returns, invoices, chasing, bookings.
- Estimator. Prices from your rates library. You check the big ones.
- Project manager. Runs several jobs, clients and subbies once you have them.
For the full hiring order and checklists, see how to get off the tools. And for the day one of them doesn't turn up: subcontractor walked off the job. And when the work isn't right: subcontractor did bad work.
Step 6: Win your first main contracts
Start with whole jobs inside the trade you know, then grow the job size. (Moving into commercial interiors? See how fit-out companies price projects.)
- Ask your current clients first. The homeowners, landlords and businesses you already work for. Offer to manage the whole job, not just your trade.
- Look like a company. A capability statement with your best projects and their values, your team, insurance and accreditations.
- Price the management. Project management, prelims and profit as lines, not hidden in the trade rates.
- Present every quote live, then follow up every week until you get a clear yes or no.
- Tender only where you fit. Public tenders that match work you have already done.
Dmitriy, a plumber for more than 20 years, won his first £50K commercial project. It came after he started presenting quotes live and following up every open quote weekly. Marek and Piter won a £450K tender in South Kensington. Individual results, not typical or guaranteed.
Dmitriy: from plumber to his first £50K commercial project
Live quote presentations and a weekly follow-up on every open quote. Individual results, not typical or guaranteed.
How Sviat helps owners make this move
Sviat Jay runs Craftex, a London main contractor, today. He mentors owners one-to-one himself, and the flagship is one-to-one mentoring by application.
The Main Contractor Accelerator (for firms at £500K+) covers finding, pricing and tendering £100K–£1M+ projects. It also covers the tender deck, cash flow, variations and hiring an estimator and a project manager. It teaches one model: the one Craftex runs on.
No two subcontractors make this move the same way. One is strong on site and weak on pricing, another sells well but has no systems. Working one-to-one, Sviat finds what you already do well and builds the main-contractor side around it. Built for results in about 4 months, not a 1–3-year program.
To see what your first main contracts could look like, book a free strategy call.
Running a trade business and ready to take whole jobs?
Book your business assessment and we'll map your first main contracts.
Before you sign your first main contract
Tax, CDM and insurance points are general information as of October 2026. Check the details with your accountant, broker or a health and safety adviser.
Ready to be the main contractor?
- Registered with HMRC as a CIS contractor, and every subbie verified
- Construction phase plan, inductions and welfare ready for the site
- Employers' liability in place, plus the cover the client's contract asks for
- Contract with stage payments, payment dates and written variations
- Cash plan that covers subbies and materials until the client pays
