Can you vary a contract without a variation clause?
Only by agreement. Without a variation clause neither party can instruct a change unilaterally, so every extra needs both parties' agreement on scope and price before it is done.
Updated: 15 September 2026. By Jack Butler-Kettle, Quantity Surveyor & Claims Consultant.
The answer
Only with the other party's agreement. A variation clause is what gives one party the power to instruct a change and obliges the other to carry it out for a valuation under the contract's rules; without one, the contract is for the scope agreed and nothing more. Extra work can still happen, but each item is a fresh agreement, ideally in writing before the work starts, that says what is to be done, for how much or on what basis, and on what dates. Work done at the other party's request without an agreed price is usually recoverable on a reasonable value, but proving the request and the value is harder than pointing to an instruction and a rate. Standard forms all contain a variation clause; the gap arises on bespoke and short-form contracts, letters of intent and purchase orders. Check before pricing the first change, not after.
Example
The situation
A purchase order covers £48,000 of joinery with no terms beyond the price and the dates. The site manager asks for a further £6,000 of skirting, and there is no variation clause to instruct it under.
What happens
- A one-page written agreement for the skirting is drawn up with its price and delivery date.
- It is signed by someone with authority on each side before the material is ordered.
- Without that agreement, the £6,000 would be a reasonable-value claim resting on emails and a request nobody signed.
The outcome
The skirting is added at £6,000 under a signed agreement rather than as a reasonable-value claim on emails and a signature-less request.
CVI & Instruction Review recovers the paper for changes that were agreed by conversation.