Read the the agreement again. It only mandates that the countries that signed the agreement wouldn't be the ones to attack Ukraine - it didn't include any obligation to defend them.

> It only mandates that the countries that signed the agreement wouldn't be the ones to attack Ukraine

Shows exactly how much international agreements are worth: One of the countries that signed the agreement was Russia.

I'm all for the UK stepping up to give Ukraine more assistance but it's not (yet) justified by the Budapest memorandum; it only guarantees assistance in the case of attack by nuclear weapons.