Generally, under English law, there is no particular formality required for making a contract.
So, even if you have a contract in writing which is signed by both parties, it’s arguable that when you want to change the terms, you can do that by a verbal agreement with the other party.
In a case earlier this year, the Supreme Court had to consider whether a telephone conversation varying the terms of a contract would be enough, when the contract itself had a clause that stated all variations must be agreed in writing and signed by both parties before they can take effect.
Surprisingly, this topic has not been considered much by the courts. So the law lords, in the case of Rock Advertising Ltd v MWB Business Exchange Centres Ltd, took their time and unanimously decided that because the variation was purportedly made on the phone, there had been no variation that complied with the contract terms.
Clauses stating that variations must be in writing are usually in the boring “boiler plate” clauses that you find at the end of the Terms and Conditions.
But those Terms can be just as important as the commercial stuff dealing with payment, delivery etc.
For more details on this case click here