For one thing, as US legal commentators have observed; what we are looking at is not a Constitution. At least, not in the way that the Americans understand it. 

A Constitution is an agreed political document describing the political structure of a country. The EU constitution has some of this, but in the main it is a Declaration of Intent; a manifesto, or a wish-list of all the powers that the EU wants. It is also a Declaration of Independence by the EU, which formally makes itself a new 'country' rather than a supra-national organisation that one chooses to belong to.

The previous, rejected constitution directly built on three previously signed treaties (Rome, Nice, Maastricht) which were to be the foundation stones of a Federation of Europe. This is an aim of which European politicians made no secret. British politicians have lied about this since the seventies.

This new attempt at a constitution, the Lisbon Treaty, does NOT simply bind together the three treaties, nor does it plug loopholes, nor is it a "simple tidying-up exercise". This is a whole new structure, deliberately made complicated, giving the EU a whole new series of legal and political powers. Again, EU politicians make no secret of this. British politicians mainly remain silent on the matter. Does anyone for one moment consider that G. Brown, Esq.actually read the thing before he sneaked around the back to sign it?.

Once the Lisbon Treaty is ratified, the conditions for withdrawal make it almost impossible for any country to ever leave the EU. The old (rejected) constitution returns, with the additional threat that the Lisbon Treaty will become self-amending. In other words, the European Commission no longer needs permission from member countries to make any change it wishes to. All restraint is removed, and it can do what it likes in the name of the European Union.

The moment Britain signs the constitution, sorry, Lisbon Treaty, we lose our voice as a major influence in world affairs. Everything will subsume to the EU cause. All Britain's international and Commonwealth holdings will become EU property.

Once we sign the constitution, we become one voice in twenty-seven or more. How many euro-laws will we succeed in overturning if they are not in Britain's interest? (Come to think of it, how many diktats have we overturned so far?)

Once we sign the constitution, any law or directive that we fail to contest will become the 'property' of the EU; we've already handed over our coal and steel, our fishing grounds, our agriculture, our county system; we are about to hand over our entire legal system and our money control...

Once we sign the constitution, if we find Brussels produces a law we do not like... tough.

Once we sign the constitution, we hand our financial controls to the EU. Our economy would be wrecked by foreign decisions we would never control. Losing the Pound sterling would be inevitable, as Lisbon states categorically that the currency of the EU will be the one-size-fits-all Euro.

Once we sign the constitution, we might as well tell the House of Commons to collect their hats and go, since our MP's would genuinely become rubber-stampers for the EU.