Firstly, the same is, I believe, true of leaving the EU which does not yet have a formal exit system, right?
(I don't spend much time studying EU treaties so forgive my ignorance if there is already such a system) Do you think that would stop us? Does promising to leave the EU make the UKIP a bunch of, to use your charming phrase, ignorant fools or shameless liars?
Well, Matt; you are, indeed, wrong. The Social Chapter cannot be repealed because it is now part of the Treaty of Amsterdam. Being an EU Treaty, the Treaty of Amsterdam requires the unanimous vote of the 27 EU countries to change it, in the Council of Ministers. OK?
In order to leave the EU, as UKIP advocate, we need simply to repeal an Act of (British) Parliament—the 1972 European Communities Act—and we are no longer in the European Union. Is that simple enough for you?
That is, of course, until we sign the EU Constitution, in which case our membership of the EU is then binding under EU Law and we cannot withdraw unless all 27 countries vote unanimously. If we decide to withdraw unilaterally, we can be fined not more than 10% of our GDP (roughly £100 billion).
Do you see why there's a time limit yet, Matt?
UPDATE: it seems that UKIP Peer, Lord Pearson of Rannoch, was thinking along the same lines.
Lord Pearson of Rannoch (UKIP) asked Her Majesty's Government:
"Whether, under international treaties presently in force, the United Kingdom would have the legal power to withdraw from the European Union if Her Majesty's Government or Parliament so resolved."
Lord Triesman (Parliamentary Under-Secretary, Foreign & Commonwealth Office)
"Parliament may amend or repeal any existing Act of Parliament, including the European Communities Act 1972. There is no formal procedure for withdrawal in the EU treaties, nor are there any provisions in the treaties or any other international obligations which affect the ultimate ability of the UK to withdraw from the EU. However, given that the UK has been a member of the EU for more than 25 years, and its laws and economy are intricately bound up with those of the EU, the Government would in practice have to negotiate the terms of any departure over a lengthy period."
So there you have it.
UPDATE 2: Bill points out that he cannot see mention of a fine. This may be the case; I was sure that I had read about penalties being imposed when I first read the Constitution some time ago, but this may not be so. I shall read it again. You can read the Constitution here and the section about voluntary withdrawal here.
However, what should be remembered is that once we sign the Constitution, all Justice and Home Affairs matters will transfer to the EU (which is already making moves to create EU-wide crimes) and should the EU wish to make withdrawal a more difficult matter, then it would be easy enough to do so.
The Constitution, whatever some people might say, is not dead. Parts of it are being pushed through under other bits of legislation anyway, and Angela Merkel has already said that she wants to make it a central tenet of the German Presidency. And just because the Dutch and French have rejected the Constitution does not mean that their government's cannot ratify it anyway. After all, the majority of those countries which have ratified the Consititution have done so without referenda.
The EU is now actively talking about a "mini-Constitutition" and Jose Barroso quite obviously believes that the Consititution must carry on.