Defining the scope of any contract is critical. It is the starting point for determining whether the goods, works and servcies provided are covered by the original contract price or require a revision to that price.
Once you’ve found out whether the change is allowed, you then need to follow the mechanism in the contract. Or do you?
A clutch of cases has looked at whether changes to a contract which did not follow the express change procedure – the bare minimum of which is often to ensure the change is recorded in writing – might still be allowed as changes to that contract.
In Globe* the contract said it “can only be amended by a written document which (i) specifically refers to the provision of this Agreement to be amended and (ii) is signed by both Parties.” The court referred to the principle of freedom to contract and said that the clause did not prevent the parties from varying the contract (including that clause about varying the contract) orally or by their conduct.
Frankly you may as well include a requirement to have the variation documents delivered on the back of a unicorn if the parties are going to ignore the procedure and the courts are going to allow that!
In Rock* the contract said “All variations to this [contract] must be agreed, set out in writing and signed on behalf of both parties before they take effect.” The Supreme Court said that the clause did prevent the parties varying the agreement by another mechanism.
They also upheld the sense that a change must meet the minimum requirements for a contract and include consideration.
What should you do? Write sensible practical contracts, that everyone can read and follow, and use the mechanisms wherever possible. But don’t rely on these clauses to wriggle out of paying for agreed changes!