One main contractor or separate trades? Structuring a London home project: legal duties, JCT home owner contracts and who controls the money

Most London home projects of any size - a side return, a loft, a basement, a top-to-bottom refurbishment of a Victorian terrace - can be procured in one of two broad ways. You can appoint a single main contractor who prices the whole job, employs or subcontracts the trades and hands the house back finished. Or you can engage separate trades yourself, sometimes with a project manager or architect co-ordinating, and pay each one directly.

Neither route is inherently honest or dishonest. But each places legal duties, risk and control of money in different hands, and a homeowner who has not settled those questions at the outset can find, when something goes wrong, that nobody accepts responsibility. This guide sets out how the rules work, which standard contracts exist and how to keep control of payments. It was checked against official sources on 20 October 2026; it is general information, not legal advice.

The two models in plain terms

A single main contractor

One firm quotes for the whole scope, organises the sequence of work, brings in its own or subcontracted electricians, plumbers and plasterers, and is answerable to you for all of it. You have one contract, one payment schedule and one party to pursue if something goes wrong. The price usually includes the contractor's management time and a margin on subcontracted trades, which is the cost of that single point of responsibility.

Separate trades

You contract directly with a groundworker, a bricklayer, a carpenter, an electrician and so on. The headline cost can look lower because there is no main contractor's margin, but you take on the co-ordination: sequencing, defining where one trade's work ends and the next begins, and resolving the inevitable arguments about who damaged what. When a defect appears at an interface - a leak where the roofer's work meets the window fitter's - it can be genuinely difficult to establish who is liable.

Your legal position as a domestic client

Two sets of rules matter, and both treat householders differently from commercial clients.

Health and safety: CDM 2015

The Construction (Design and Management) Regulations 2015 apply to domestic work. The Health and Safety Executive explains that a domestic client's duties normally pass to someone else:

• on a single-contractor project, to that contractor, who takes on the client duties in addition to its own;
• where there is more than one contractor, to the principal contractor - and if you have not appointed one, to the contractor in control of the construction work;
• alternatively, if you have appointed an architect or other designer on a multi-contractor project, to that designer as principal designer, but only if there is a written agreement with you to that effect.

Larger projects must also be notified to the HSE on form F10. Under regulation 6 of CDM 2015, notification is needed where construction work is expected to last more than 30 working days and have more than 20 workers on site simultaneously at any point, or to exceed 500 person-days. For a domestic client, that duty passes with the client duties.

Building Regulations: the dutyholder regime

Since October 2023, the Building Regulations in England have carried their own dutyholder roles, introduced by the Building Regulations etc. (Amendment) (England) Regulations 2023. GOV.UK's guidance on meeting building requirements says a domestic client must allow enough time and resource for the work to comply, appoint designers and contractors, co-operate with them and provide the building information they hold or could reasonably obtain, such as previous surveys.

Where several designers and contractors are involved and you do not appoint a principal designer or principal contractor, the guidance says the designer in control of the design phase becomes principal designer and the contractor in control of the construction phase becomes principal contractor by default. The practical lesson for anyone hiring separate trades is clear: if you do not decide who is in charge and write it down, the law will decide for you, and the person it picks may not realise it.

Standard contracts written for homeowners

Whichever model you choose, a written contract is the single most effective protection you can buy. The Joint Contracts Tribunal publishes two home owner forms, both updated in its 2021 edition:

• HO/B 2021 - for a homeowner or occupier dealing directly with the contractor without a consultant. JCT describes it as suitable for small domestic work such as extensions and alterations, for an agreed lump sum paid on completion or by agreed interim payments. Part 1 covers the work, planning, Building Regulations and party walls, price, payment, working period, insurance and working hours; Part 2 covers changes, extensions of time, insolvency and ending the contract.
• HO/C and HO/CA 2021 - a building contract plus a consultancy agreement, for projects where an architect or surveyor administers the contract on your behalf.

JCT also notes that, as consumer contracts for a residential occupier, these are excluded from the statutory adjudication provisions of the Construction Act, but the forms themselves provide for adjudication if a dispute arises. That is worth knowing: a homeowner who signs a builder's own one-page terms may have no quick dispute route at all.

If you hire separate trades, each needs its own written terms. Insist that each contract names the scope precisely, refers to the same drawings and specification, and states who is responsible for protecting finished work from the next trade.

Who controls the money

Payment structure is where honest projects stay honest. Citizens Advice recommends not paying everything up front, keeping any deposit as low as possible and not agreeing to more than 25 per cent, getting a receipt, and considering deposit insurance or an FCA-registered escrow service where a larger sum is unavoidable.

With a main contractor, tie each payment to a stage you can see and verify:

1. a modest deposit, ideally against identifiable materials or scaffolding;
2. foundations or structural work signed off by building control;
3. the shell weathertight;
4. first fix complete;
5. plastering and second fix complete;
6. a final sum held back until snagging is finished and the completion certificate and trade certificates are in your hands.

With separate trades, the risk is different. Each trade will want paying as soon as its part is done, and you may find yourself funding a plasterer before the electrician has certified the wiring behind the plaster. Hold back an agreed amount from each trade until the dependent trade has followed on without problems, and never pay for a trade's materials into a personal account in a different name from the business on the quote.

For a single item costing more than £100 and no more than £30,000, paying at least part by credit card can give you a claim against the card provider under Section 75 of the Consumer Credit Act, according to Citizens Advice. Many builders do not take cards, but some suppliers do.

Vetting whoever is in charge

Whether you appoint one firm or several, check each of them before money changes hands:

• Companies House - for limited companies, confirm the name and number on the quote match the public register, look at the incorporation date and check the directors' other appointments for a pattern of dissolved companies.
• Insurance - ask for current public liability and, where they employ staff, employer's liability schedules in the business's own name. Ask your own home insurer whether the works affect your cover.
• Registers, not logos - check TrustMark, and for gas or notifiable electrical work the Gas Safe Register and NICEIC or NAPIT. A main contractor who subcontracts these trades should give you the subcontractors' names so you can check them too.
• Visible past work - ask to speak to two or three recent London clients and, ideally, to see a finished project in person.

Red flags specific to each model

With a main contractor

• a price far below the others with no explanation of what has been left out;
• reluctance to name the subcontractors for gas, electrics or structural steel;
• a request for a large "materials" payment before any programme has been agreed;
• no written contract, or terms that make every change a verbal arrangement.

With separate trades

• no one willing to accept the principal contractor role in writing;
• each trade working from different drawings, or none at all;
• trades arriving out of sequence because a previous one overran;
• gaps in insurance - a sole trader with no liability cover working at height on a London terrace is a real exposure.

Your rights if the work goes wrong

The Consumer Rights Act 2015 requires a trader to perform a service with reasonable care and skill (section 49); things the trader tells you before the contract can become binding (section 50); and if no time is fixed, the work must be done within a reasonable time (section 52). If the service falls short, you can ask the trader to put it right or, where that is impossible or not done within a reasonable time, seek a price reduction.

Keep a dated photographic record of each stage, put complaints in writing, and refer to Citizens Advice guidance on problems with home improvements before you withhold money or bring in another firm to finish. If you signed a JCT home owner form, follow its dispute clauses, including adjudication.

Which route suits which project?

As a general guide, a single main contractor under a written contract tends to suit structural and multi-trade work - extensions, lofts, basements and full refurbishments - where interfaces between trades are numerous and the legal duties are substantial. Managing separate trades can work for smaller, sequential jobs where each trade's scope is self-contained, or where an architect or project manager is formally appointed to co-ordinate. Whichever you choose, settle three things in writing before work starts: who is the principal contractor, which contract governs the work, and exactly when each payment becomes due.

Sources (checked 20 October 2026): HSE, Domestic clients: roles and responsibilities; CDM 2015, regulation 6; Building Regulations etc. (Amendment) (England) Regulations 2023; GOV.UK, Design and building work: meeting building requirements; JCT, HO/B 2021; JCT Home Owner Contracts 2021; Citizens Advice, Before you get building work done; Citizens Advice, Section 75 and chargeback; Consumer Rights Act 2015. Nothing here is legal advice.