It's a bit of a mess, actually

Remember the Lisbon Treaty? The lovely Tamzin explains the Tory position:

Mr Hague has gone to exhaustive lengths to explain what he means when he says he can’t say whether or not he will say what he means when he says he can’t say what we will do if the Lisbon Treaty passes into law before we get into government, or not. To recap from the briefing notes: ‘“We will not let matters rest there” is a hypothetical holding answer to the hypothetical question of whether or not we will do something about a situation in the future we want to prevent happening in the first place and as such we can only answer a question pertaining to the opposite turning out to be the case because to do otherwise would be to elaborate on the unknowable.

Oh Sir Humphrey, thou shouldst be living at this hour ...