Contract Variation: How to Change a Contract Legally in the UK

Business relationships rarely stand still. Prices move, suppliers change, projects grow, and the deal you signed two years ago stops matching how you work together. A contract variation is how you bring the written terms back in line with reality, without tearing up the agreement and starting again.

Done properly, a variation of contract is quick and low risk. Done casually, through a phone call, a vague email or a new way of working that everyone just starts following, it can leave you arguing later about which terms apply.

This guide covers what a contract variation is, what makes one valid in England and Wales, no oral modification clauses, consideration and deeds of variation, employment contracts, and a step-by-step process for varying a contract safely.

What is a contract variation?

A contract variation is an agreed change to the terms of an existing contract. The original agreement stays in force, and only the terms you change are updated. Almost anything can be varied if both sides agree, including:

• price, payment terms or invoicing arrangements
• the scope of work, specifications or deliverables
• delivery dates, timelines and service levels
• the length of the contract, renewal terms or notice periods
• liability caps, warranties and indemnities
• schedules, such as a product list or rate card

A variation is not a new contract. You may see it called an amendment, an addendum, a variation agreement or a variation letter. The label matters far less than what the document says and how it is signed.

There is a limit, though. If the change is so fundamental that it alters the whole purpose of the deal, a court may treat the original contract as having been replaced by a new one. At that point, varying it may not be the right tool, which we cover further below.

When is a variation of contract legally valid?

Both parties agree

Varying a contract is a two-way process. One party cannot simply notify the other that the terms have changed, and silence is not acceptance. Sending an updated price list and hearing nothing back does not mean the customer has agreed to it.

The exception is where the contract itself gives one party a right to make certain changes on its own, often called a unilateral variation clause. Even then, the change is only valid within the limits of the clause, which usually sets out notice periods, what can be changed and sometimes a right for the other party to walk away. If you are being asked to sign a contract that gives the other side a broad right to change important terms, that is worth pushing back on before you sign.

You follow the contract’s variation clause

Most well drafted commercial contracts include a variation clause setting out how changes must be made. Typically, changes must be in writing and signed by or on behalf of both parties. Some contracts, particularly longer projects, use a change control procedure with its own forms and approval steps. Whatever your contract says, follow it exactly.

There is consideration, or it is made as a deed

Under English law, a promise is generally only binding if each side gives something of value in return, known as consideration. A variation is no different. If one side is getting nothing in exchange for the change, the safer route is a deed. Both points are explained in more detail below.

The people agreeing have authority

The person agreeing the change must have the authority to bind their business. An account manager agreeing a new price on a call may not have that authority, and a variation signed by the wrong person can be challenged later. Check who is signing on both sides, and whether your contract or your internal approval rules require a director.

The change is intended to be permanent and agreed freely

A variation changes the contract going forward. A temporary favour, such as letting a customer pay late once, is not the same thing. The agreement must also be given freely. A variation extracted through improper pressure, such as a threat to stop supplying unless a price rise is accepted immediately, risks being set aside for economic duress.

Ways to vary a contract: in writing, orally or by conduct

Where the contract and the law allow it, there are three ways a contract can be varied:

• In writing. A signed variation agreement or letter. This is the most reliable method because there is a clear record of exactly what was agreed and when.
• Orally. A change agreed on a call or in a meeting. It can be binding where the contract does not require writing, but it is hard to prove if the relationship later breaks down.
• By conduct. Where both parties behave consistently with new terms over time, for example a supplier accepting payment on 45 days for months when the contract says 30. Whether that amounts to a variation, or just tolerance of a breach, is often unclear and easily disputed.

No oral modification clauses: what the law says now

Many commercial contracts include a clause saying the contract can only be varied in writing and signed by both parties. This is known as a no oral modification (or no oral variation) clause.

For years, the position was unclear. Court of Appeal decisions suggested that parties could agree orally to ignore such a clause, and some older guidance online still says this. That changed in 2018. In Rock Advertising Ltd v MWB Business Exchange Centres Ltd [2018] UKSC 24, the Supreme Court confirmed that no oral modification clauses are effective.

The case involved a serviced office licence. The occupier fell into arrears and said it had agreed a revised payment schedule with the provider’s credit controller over the phone. The licence required any variation to be in writing and signed by both parties. Because the new arrangement had not been agreed that way, the Supreme Court held it did not vary the licence. The court’s view was that parties who ignore such a clause have usually overlooked it, not decided to set it aside.

There is a narrow safety valve. If one party clearly represents that an informal change is valid and the other relies on it, the first party may be prevented from relying on the clause, under a principle called estoppel. The Supreme Court set a high bar for this, requiring more than the informal promise itself.

The takeaway: if your contract has a no oral modification clause, assume calls, messages and loose email chains will not change it. Put the change in writing and sign it as the clause requires.

Does a contract variation need consideration?

A variation made as an ordinary contract needs consideration. In practice, this usually means each side gets something out of the change. For example, a supplier agrees to bring delivery forward and the customer agrees to pay a premium, or a customer accepts a price rise in return for a longer fixed term.

Problems arise with one-sided changes. If a supplier agrees to do more work for the same price, or a business agrees to accept less than it is owed, the party making the concession may later argue it received nothing in return.

The courts have softened this rule in some situations. In Williams v Roffey Bros & Nicholls (Contractors) Ltd, the Court of Appeal accepted that a practical benefit, such as getting a job finished on time and avoiding penalties, could count as consideration even where one party agreed to pay more for the same work. The courts have been more cautious where a creditor agrees to accept less money than it is owed. Relying on practical benefit is therefore an argument you may be able to make later, not a plan.

If there is no clear exchange of value, the safer approach is to record the change as a deed.

When to use a deed of variation

A deed is a formal legal document that is binding without consideration. That makes a deed of variation the right choice where:

• one party is making a concession and getting nothing clear in return
• the original agreement was itself executed as a deed, such as a guarantee
• the change affects guarantees, releases or security
• the contract requires amendments to be made by deed
• you simply want to remove any argument about enforceability later

Deeds have strict signing rules and getting them wrong is one of the most common reasons a variation fails. The document must make clear on its face that it is intended to be a deed. A company can execute a deed by the signatures of two authorised signatories (a director or the company secretary), or by one director signing in the presence of a witness who attests the signature, under section 44 of the Companies Act 2006. An individual must sign in the presence of a witness who attests the signature, under section 1 of the Law of Property (Miscellaneous Provisions) Act 1989. The witness should be physically present when the document is signed, and it is good practice to use someone independent.

Can you vary a contract by email?

Sometimes, but it is risky. Whether an email exchange varies a contract depends on:

• whether the contract requires variations to be in writing and signed, and whether the emails meet that requirement
• whether the wording is clear enough to show exactly what was agreed
• whether the people sending the emails had authority to agree the change

Courts have sometimes treated a typed name or email sign-off as a signature, but the outcome turns on the facts. A thread ending in “happy to go with that” rarely shows precisely which terms changed and from when.

For anything that matters, such as price, scope, liability or duration, use a short variation document and sign it properly. Electronic signatures are generally valid for ordinary contracts, but a deed must still meet the witnessing and execution requirements above.

Variation, novation, waiver or a new contract?

Not every change should be handled as a variation. It helps to know the alternatives:

• Variation: the same parties agree to change some of the terms. The rest of the contract carries on as before.
• Novation: a new party replaces one of the original parties, for example when a contract moves to a different group company or a buyer of your business. This needs the consent of everyone involved and is usually documented in a separate novation agreement. A variation cannot do this.
• Waiver: one party chooses not to enforce a right, often on a one-off basis, such as accepting a late payment this month. A waiver does not necessarily change the contract, but repeated tolerance can blur the position. If you are making a one-off concession, say so in writing and check whether the contract has a no-waiver clause.
• New or restated contract: if you are changing a large part of the agreement, or it has already been varied several times, a fresh agreement (or an amended and restated version of the old one) is often cleaner than stacking variation on variation.

If you have a right to terminate and a strong bargaining position, ending the contract and negotiating afresh can get you better terms, but it can also unsettle the relationship and reopen points you would rather keep closed.

How to vary a contract: a step-by-step process

Whether you are a Manchester start-up updating a supplier agreement or an established business renegotiating a key customer contract, the same process applies.

1. Pin down exactly what is changing and why, including the commercial trade-off.
2. Read the existing contract.Look for the variation clause, any no oral modification wording, change control procedures, notice requirements, consent requirements, third party rights, and upcoming renewal or termination dates.
3. Think about the knock-on effects. A wider scope may mean your liability cap or insurance no longer fits. A price change may need updated schedules. A concession to one customer may create pressure to offer the same to others.
4. Get internal sign-off from finance, operations or the board, depending on the contract’s value.
5. Choose the right document: a variation agreement, a deed, a novation or a new agreement.
6. Draft precise wording that refers to clause numbers, then sign it with the right signatories and formalities.
7. Store it and tell people. Keep the signed variation with the original contract and make sure the teams invoicing and delivering against it know what has changed and from when.

What should a contract variation agreement include?

There is no single required format, but a clear contract variation agreement usually covers:

• the full legal names of the parties, with company numbers where relevant
• the original contract, identified by title, date and parties, and any earlier variations
• the date the changes take effect
• the precise amendments, clause by clause
• any new or replacement schedules
• the consideration given, or wording confirming it is executed as a deed
• confirmation that all other terms remain unchanged and in full force
• which document takes priority if the variation and the original conflict
• signature blocks that match the contract’s requirements

Precise wording avoids arguments later. A clause might read: “With effect from 1 March 2027, clause 6.1 of the Agreement is deleted and replaced with: ‘The Customer shall pay each invoice within 45 days of the invoice date.’ Except as set out in this Variation Agreement, the Agreement remains unchanged and in full force and effect.”

Varying employment contracts

Employment contracts follow the same basic principle, that changes need agreement, but with extra rules. Changes to an employee’s terms usually happen in one of four ways: by agreement with the employee, through a collective agreement with a recognised trade union, under a flexibility or variation clause in the contract, or occasionally through established custom and practice. Courts tend to read flexibility clauses narrowly, so they rarely justify significant changes to pay, hours or duties.

When a change is agreed, section 4 of the Employment Rights Act 1996 requires the employer to give the employee a written statement of the change at the earliest opportunity, and no later than one month after the change takes effect.

Imposing changes without agreement is high risk. It can lead to breach of contract and constructive dismissal claims, as well as damaging morale. Dismissing employees and re-engaging them on new terms, often called fire and rehire, is subject to a statutory Code of Practice and is being further restricted under the Employment Rights Act 2025. Consult properly and take advice before going anywhere near it. Our employment law team regularly helps employers across Manchester and the UK plan contract changes and put them in writing correctly.

Don’t forget third parties

Some contracts give rights to people who are not parties to them, such as a group company or a named beneficiary. Under section 2 of the Contracts (Rights of Third Parties) Act 1999, if a third party has an enforceable right, you cannot vary the contract to remove or change that right without their consent where they have told the promisor they accept the term, where the promisor knows they have relied on it, or where reliance was reasonably foreseeable and has happened. Many contracts exclude the Act altogether, so check the boilerplate clauses.

Guarantees need particular care. If someone has guaranteed a party’s obligations, varying the main contract without the guarantor’s agreement can risk releasing them, unless the guarantee allows for variations. The simplest fix is to have the guarantor confirm their consent in the variation itself.

If you trade with consumers, broad rights to change terms on your own can be unfair and unenforceable under the Consumer Rights Act 2015.

Common contract variation mistakes to avoid

• Treating informal changes as settled, especially where there is a no oral modification clause.
• One-sided concessions without a deed, leaving the variation open to challenge for lack of consideration.
• Vague drafting, such as “the scope will increase as needed”, instead of clause-by-clause wording.
• The wrong signatory or execution method, including deeds signed without a proper witness.

Losing track of versions, with several variations stacked on an old contract and stored in different inboxes.