What property professionals need to know about getting contract variations right

Contract variations are a fact of life in property transactions. A tenant wants to alter their permitted use. Development timelines shift and payment schedules need adjusting. A conditional contract requires amendment before completion. These changes happen regularly, and when relationships are good, the temptation is to agree them quickly and informally.

A recent High Court decision demonstrates why that approach can be costly. In GSY Hospitality Ltd v Gladstone Court Developments Ltd, an informal agreement to vary a development contract was held to be invalid, leaving one party significantly worse off than they believed. The reason for this was simple. The parties hadn’t complied with their own contract’s requirements for making variations.

Why variation clauses matter

Most well-drafted property agreements contain what’s known as a no oral modification clause. These provisions specify exactly how the contract can be changed, typically requiring any variation to be made in writing, signed by both parties or their solicitors, and be compliant with the Law of Property (Miscellaneous Provisions) Act 1989 for agreements concerning land. A standard clause might read: “This Agreement may only be varied by a supplemental agreement in writing signed by or on behalf of each party.”

These aren’t mere formalities. They exist because property transactions are complex, high-value, and often span years. Clear documentation of any changes protects both parties by eliminating later disputes about what was agreed, when, and on what terms.

Do these clauses actually have teeth? Many people assume that if both parties genuinely agreed a change and acted on it, the courts would recognise that reality over technical requirements. The legal position is rather different. The Supreme Court has made clear that these clauses are enforceable, and courts will not assume parties intended to waive formal requirements simply because they failed to follow them. If parties overlook the variation clause rather than deliberately choosing to ignore it, the informal variation is invalid.

This means that even where both parties genuinely believe they’ve agreed a change, and even where both parties act consistently with that understanding, the variation won’t be legally effective if it doesn’t comply with the contractual requirements.

In the GSY Hospitality case, a developer convinced an expert that the parties had orally agreed to cap the developer’s cost liability at £800,000. The purchaser had never challenged interim payment applications referring to this cap, which surely demonstrated mutual agreement. The High Court disagreed. The contract contained a clear no oral modification clause, the oral agreement didn’t comply with it, and the variation was therefore invalid regardless of the parties’ conduct or mutual understanding.

Where informal variations cause problems

The scenarios where this ruling matters are familiar to anyone involved in property work. Development agreements often need changes to specification, phasing, or cost allocation as projects progress. These are frequently agreed during site meetings or via email exchanges, but may not be formally documented until much later, if at all.

Lease agreements may require variations to permitted use, alterations provisions, or rent review mechanisms, with landlords and tenants reaching pragmatic agreements without realising their lease requires formal documentation. Option and conditional contracts are often amended while parties work toward completion, and the informal nature of ongoing negotiations can obscure the need for proper variation agreements. Even management and service agreements commonly see changes to specifications or payment terms in response to practical experience, and where relationships are good, these often proceed on a handshake basis.

In each case, proceeding informally creates risk. The party who believes they’ve secured a beneficial variation may find they cannot enforce it, while the party who believed they’d agreed to a change may find themselves still bound by the original terms.

Can conduct save an informal variation?

A common response when informal variations are challenged is to point to the parties’ conduct. If we’ve both acted as though the variation was agreed, how can one party now deny it? The legal position offers limited comfort. While arguments based on estoppel or waiver might provide protection in exceptional circumstances, the bar is high. You will need to show that one party unequivocally represented the informal variation was valid despite not following required formalities, that the other party took substantial steps in reliance on that representation beyond merely performing the informal promise itself, and that it would be unconscionable to allow the first party to resile from the variation. Simply proceeding based on what you both understood to be agreed is unlikely to be enough, and proving these elements will likely require expensive, time-consuming litigation with an uncertain outcome.

How to document variations properly

The solution is more straightforward than many people assume. Before agreeing any change, check your agreement for variation provisions and identify what formalities apply. This might include requirements for written agreement, specific signatures, or even witnessing or notarisation in some cases. Confirm who has authority to agree variations on behalf of each party.

When documenting the variation, prepare a written agreement that clearly identifies the original contract, specifies precisely what is being changed by reference to clause numbers where possible, states that all other terms remain unchanged, and ensures the variation is signed by appropriate representatives of both parties. For agreements concerning land, ensure compliance with section 2 of the Law of Property (Miscellaneous Provisions) Act 1989.

Sometimes commercial or practical pressures mean you need to proceed before formal documentation can be prepared. A critical deadline might be missed, or works need to commence immediately to avoid delay costs.

If you genuinely cannot comply with variation requirements immediately, create detailed contemporaneous records through meeting minutes or emails that explicitly acknowledge the variation clause and record both parties’ intention that the informal arrangement should have immediate effect. State clearly that formal documentation will follow as soon as possible, and then actually prepare and execute that formal documentation promptly. Be aware this remains a risk. If the relationship deteriorates before formal documentation is completed, you may find the variation is unenforceable.

The far better approach is to build time for proper documentation into your planning, agreeing changes early enough that formal documents can be completed before you need to rely on them.

The cost of getting it wrong

The GSY Hospitality case involved a claimed variation that would have capped liability at £800,000. When that variation was held invalid, the developer faced significantly higher costs under the original contract terms. The case then proceeded to litigation over expert determination and summary judgment applications, and will likely continue to a full trial on the estoppel issues. The cost of preparing a proper variation agreement? A few hours of legal time. The cost of proceeding informally? Potentially hundreds of thousands of pounds in additional liability, plus substantial legal and funding costs, management time, and reputational damage.

Property agreements require flexibility. Circumstances change, parties need to adapt, and commercial relationships depend on pragmatism. Remember flexibility must operate within the contractual framework you’ve agreed. If your contract contains a variation clause, it’s there for a reason – it protects both parties by ensuring clarity about what’s been agreed. Complying with it isn’t bureaucracy, it’s essential risk management. When you need to vary a property agreement, take the time to do it properly. Check your contract’s requirements, document the change formally, get appropriate signatures, and keep clear records. Your future self will thank you.