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Construction Subcontracts UK: Key Terms Explained

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Part ofUK Property Law Guide

Written by Brad Askew Solicitor (non-practising)
Brad is on the roll of solicitors of England & Wales but does not hold a practising certificate and does not provide legal advice.
Updated June 2026 · England & Wales
On almost every construction project of any real size, the company named on the main contract is not the company doing every part of the work. Specialist trades, from groundworks to mechanical and electrical fit-out, are typically brought in under a separate arrangement sitting underneath the head contract. That separate arrangement is the subcontract. It governs who does what, who pays whom, what happens if something goes wrong, and how the subcontractor's obligations line up with what the main contractor has promised the employer. Getting that alignment right matters, because gaps between the two contracts tend to land on whoever signed the subcontract without reading it carefully. This page walks through how subcontracts operate in the UK construction sector, the clauses that tend to cause disputes, and the wider issues worth thinking through before you commit.

What this document is

A subcontract is a contract between the main contractor (who holds the head contract with the client or employer) and a third party who agrees to carry out a defined part of the works. The main contractor remains on the hook to the employer for the whole project.

The subcontractor is on the hook to the main contractor for the slice of work they have taken on. In practice, a well-drafted subcontract will set out the scope of works, the price and how it gets paid, the programme and any key dates, quality standards, insurance requirements, how variations are handled, what happens on delay or termination, dispute resolution, and the governing law.

In the UK, subcontracts in construction are also shaped by statute, particularly the payment and adjudication provisions in the Housing Grants, Construction and Regeneration Act 1996 (as amended). Standard form subcontracts, such as those in the JCT and NEC suites, are commonly used because they are designed to dovetail with the main contract forms those families publish.

How to use this document

  1. Read the main contract alongside the subcontract. Before signing anything, ask to see the relevant parts of the head contract. A subcontract often pulls obligations down from above, and you cannot sensibly agree to 'back-to-back' terms without knowing what sits on top. Mismatches between the two documents are a common source of later disputes.
  2. Pin down the scope of work precisely. Vague descriptions of what is and is not included almost always bite later. Specify drawings, specifications, revisions, exclusions, and any assumptions about what other trades will have done first. The narrower and clearer the scope, the easier it is to price variations when things change on site.
  3. Check the payment mechanism against the Construction Act. UK construction contracts must include an adequate mechanism for determining what is due and when, along with a right to suspend for non-payment and a right to refer disputes to adjudication. If the contract is silent or non-compliant, the Scheme for Construction Contracts fills the gaps. Pay-when-paid clauses are generally unenforceable except in narrow insolvency scenarios.
  4. Sort out insurance, warranties and security. Work through professional indemnity cover, public liability limits, parent company guarantees, performance bonds, and any collateral warranties owed to the employer, funder, or future tenants. These are often non-negotiable from the main contractor's side because they flow from the head contract, so build the cost into your price.
  5. Agree how disputes will be handled. Adjudication under the Construction Act is a statutory right and cannot be contracted out of. Beyond that, think about whether final determination will be by litigation or arbitration, and whether any tiered process, such as mediation first, is workable for the sort of disputes that realistically arise on this project.

Common questions

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Common questions

Q What is the difference between a main contract and a subcontract?
The main contract, sometimes called the head contract, is between the employer or client and the main contractor. The subcontract sits underneath it and is between the main contractor and a specialist or trade contractor carrying out part of the works. The subcontractor has no direct contractual link with the employer unless a collateral warranty or third party rights clause creates one.
Q What does 'back-to-back' mean in a subcontract?
A back-to-back subcontract is drafted so the subcontractor's obligations mirror, as far as possible, the obligations the main contractor owes under the head contract. The idea is that risk passes straight down the chain. In practice, perfect alignment is rare, and subcontractors should always check what is actually being passed down rather than assuming it is reasonable.
Q Are pay-when-paid clauses allowed in UK construction contracts?
Generally no. The Housing Grants, Construction and Regeneration Act 1996 renders pay-when-paid clauses ineffective in most construction contracts, with a narrow exception where the paying party up the chain is insolvent. Main contractors cannot usually make payment to a subcontractor conditional on first being paid by the employer.
Q What is a collateral warranty and why do subcontractors sign them?
A collateral warranty is a separate agreement giving a third party, often the employer, funder, purchaser, or tenant, a direct contractual right against the subcontractor. It lets that third party bring a claim directly if the subcontractor's work is defective, rather than having to route through the main contractor. They are common in commercial construction projects.
Q Can a subcontractor refer a dispute to adjudication?
Yes. The statutory right to refer a construction dispute to adjudication at any time applies to subcontracts as well as main contracts. Adjudication produces a decision that is binding on an interim basis and must usually be complied with, even though either party can later pursue the matter in court or arbitration for a final ruling.
Q Does the main contractor remain liable for the subcontractor's work?
Yes. Subcontracting does not transfer the main contractor's obligations to the employer. If the subcontractor's work is late or defective, the employer's claim is still against the main contractor under the head contract. The main contractor would then typically look to recover from the subcontractor under the subcontract.
Q Which standard form subcontracts are commonly used in the UK?
The JCT suite includes subcontracts designed to sit beneath its main contract forms, such as the JCT Standard Building Sub-Contract. The NEC family offers the NEC Subcontract. FIDIC also publishes subcontract forms used on international projects. The right choice usually depends on which form governs the main contract and the size and complexity of the project.
If you're dealing with this kind of situation, speak to an experienced legal adviser who can walk you through it — from £89.

Sources

This guide is based on primary UK law and official guidance.

Brad Askew, Solicitor (non-practising)

Written & reviewed by

Brad Askew Solicitor (non-practising)

Brad is on the roll of solicitors of England & Wales but does not hold a practising certificate and does not provide legal advice. LegalDocuments.co.uk is not a law firm and does not provide regulated legal advice.

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Legal disclaimer
This article is for general information only. It is a tool to help you find your way — not legal advice, and not a substitute for speaking to a qualified adviser about your situation.