In a judgment handed down today in Rock Advertising Ltd v. MWB Business Exchange Centres Ltd  UKSC 24, the Court held that there was no reason why parties could not restrict themselves as to the way in which their obligations could be varied. Lord Sumption, who gave the leading judgment, left open the possibility that an estoppel might arise to prevent reliance on such a clause where there were some words or conduct unequivocally representing that the variation was valid. However, the informal variation itself would not suffice.
The Court declined to rule on the question of whether a variation of a contract to pay either less money or the same money later could be valid consideration for a variation. Lord Sumption said that consideration of that question would require a larger panel of the Court.
Lord Briggs gave a judgment which dissented from Lord Sumption’s reasoning but did not dissent from the result. He held that parties should be able to reach express oral agreement to dispense with such a clause.