By Nick Assinder
Political Correspondent, BBC News website
The battle over the EU constitution may have only just swung into action, but already it is mired in controversy.
EU constitution battle is joined
Government statements have appeared to offer contradictory messages over whether or not there would be a UK referendum on the treaty, whatever other countries decide.
Europe minister Douglas Alexander has finally clarified what most have long believed, and what must be glaringly obvious - there will only be a vote in Britain if there is a constitution to vote on.
Speaking on the BBC's Today programme, he said: "As the Prime Minister has made clear on a number of occasions, as long as there's a treaty to vote on, we intend to have a referendum".
In other words, if the French vote no - and it is too close to call at the moment - and spark a crisis over the constitution, the debate in Britain may be killed stone dead as EU leaders scramble back to the drawing board.
Needless to say, that will not find favour with the Tories who are pressing for a vote come what may, presumably on the grounds that is the only way of killing off the entire project without any prospect of it being revived in the future.
Shadow Foreign Secretary, Liam Fox, has demanded the government sets a date for that vote now, declaring: "There's no guarantee that if a country votes no, they won't be bullied into voting yes in a subsequent referendum".
Meanwhile, the prime minister's official spokesman has said that, while the government's position remains unchanged, the result of the French referendum would "establish the context" of the UK campaign.
And that context is that if one of the biggest and most influential countries in the EU rejects the treaty, leaders across the union will fear their electors will be encouraged to follow suit.
They will, therefore, look instead for a way out of the crisis that would inevitably follow.
French no vote is crucial to UK
Many believe the most likely outcome would be a decision to withdraw the constitution.
That could be debated at the EU summit in Brussels in the middle of June and then be followed by a special Inter Governmental Conference (IGC) to resolve the issue.
The timing is sensitive for the prime minister as he takes over the rotating presidency of the EU in July and may find the whole affair dropped into his lap.
There are, of course, wider consequences for Mr Blair, whatever the outcome in France.
A yes vote means a certain referendum in Britain next spring, or thereabouts, with the prime minister looking to a similar result here to forge part of his legacy.
But there is always the huge danger, experienced to a large degree in France, that the referendum turns into an unofficial vote on something quite different - specifically Tony Blair's premiership.
Those who believe, rightly or wrongly, that the general election outcome suggested voters wanted Labour but not Blair would certainly attempt to use the referendum as a way of achieving just that.
Alternatively a no vote in France may well prompt his party detractors into moving against him straight away.
Either way, the worrying implication for both the newly-launched no campaign and the yes movement is that arguments over the relative merits of the constitution may be overwhelmed by the debate about the prime minister's future.