Types of Contracts in UK Law

Rectification is concerned with contracts and documents, not with intentions. In order to got rectification, it is necessary to show that the parties were in complete agreement on the terms of their contract, but by an error wrote them down wrongly; and in this regard, in order to ascertain the terms of their contract, you do not look into the inner minds of the parties – into their intentions – any more than you do in the formation of any other contract.

At the very least, (i) there would have to be some words or conduct unequivocally representing that the variation was valid notwithstanding its informality; and (ii) something more would be required for this purpose than the informal promise itself: see Actionstrength Ltd v International Glass Engineering In Gl En SpA [2003] 2 AC 541, paras 9 (Lord Bingham), 51 (Lord Walker).

The confusion is caused by the fact that the term "consideration", when used in the phrase "total failure of consideration" as a reason for restitution, does not mean quite the same thing as it does when considering whether there is sufficient "consideration" to support the formation of a valid contract. Viscount Simon LC, explained this in Fibrosa Spolka Akcyjna v Fairbairn Lawson Combe Barbour Ltd [1943] AC 32, 48:

Whereas an oral contract was allowed and enforceable provided that it was evidenced in writing and the memorandum or note thereof was signed by or on behalf of the party against whom it was sought to be enforced, oral contracts are now of no effect and all contracts must be signed by or on behalf of all the parties.

I do not regard the decision in Yam Seng Pte Ltd v International Trade Corporation as authority for the proposition that in commercial contracts it may be taken to be the presumed intention of the parties that there is a general obligation of "good faith". Boots was not obliged as a matter of "good faith" to order from Hamsard goods that it did not want (the so called "transitional AW10 stock") simply because if it had done so the nascent joint venture would have been more profitable.

As counsel for Matchmove accepted, however, it is important not to construe this paragraph of Arden LJ's judgment as if it were a statute. In our judgment, Arden LJ was not intending to describe three different situations in which section 2(5) would not apply, but rather to describe Cobbe in three different ways.

So perhaps it would be simpler to say at the outset that frustration occurs whenever the law recognises that without default of either party a contractual obligation has become incapable of being performed because the circumstances in which performance is called for would render it a thing radically different from that which was undertaken by the contract.