Private reason why PM could be happy to lose

The fascinating thing about Tony Blair's decision to hold a vote on the EU constitution is that he really could lose.

Today's poll in The Sun newspaper, claiming opposition to the treaty is running at three-to-one, indicates a mountain to climb to change widespread hostility. Moreover, the campaign against the constitution is well organised and crosses the party divide.

By holding a vote early in the next parliament, when his own career will be drawing to a close and the election danger point is past, Mr Blair can count less on his personal sway than usual.

So why should Mr Blair, still a barrister at heart, break the normal rules of engagement by asking a question in the "court" of public opinion when he cannot guarantee getting the answer he wants in reply? The official reason is that he fears being wrong-footed by the Tories in the June elections and the general election next year.

But this is not fully convincing, firstly because the European elections have already been written off by Labour, secondly because it is a New Labour nostrum that voters let off steam about Europe in the opinion polls but vote about schools and hospitals when their X really counts, in the polling booth on election day.

In private, a more intriguing reason is floated by some Labour MPs. They suggest Mr Blair is not really as keen on the EU constitution as he has appeared in recent months and, while unwilling to say no to his EU partners at Brussels, would not mind much if the plan was ruled out by the British people. That way, he could be both a "good European" and avoid a treaty which contains pitfalls.

Certainly, Cabinet ministers appeared frankly relieved when the constitution negotiations broke down before Christmas and were aghast when the new Spanish government put the project back on track.

An alternative theory is that Mr Blair may see a vote on the constitution as a dress-rehearsal for a future referendum on the single currency. The Prime Minister is unlikely to be around long enough to be in charge when any vote on the euro is held but he remains an enthusiast. Proving to his more nervous colleagues that the Tory-led eurosceptics can be routed at the ballot box would be a huge advance for the pro campaign.

Whenever the EU crops up in conversations with Downing Street aides and ministers, the theme that repeatedly comes up is of winning the wider battle about Europe. The idea that there is a fundamental debate to be had over whether Britain is in or out is almost an obsession with the Government.

It points to a deep-seated insecurity about Britain's place in the EU. While sceptics see a ratchet effect, where every treaty cements the federalist advance, the Government sees a much more unstable situation where a drizzle of anti-EU propaganda has injected doubt and uncertainty into the minds of the public. A referendum would transform the Government's confidence in future debates.

Whatever Mr Blair's true private motives, the fact remains obvious that this U-turn has been forced on him in the face of all his instincts and a string of past comments ruling out a referendum. If he wins, the short-term embarrassment will be worthwhile. But the added impression that the Prime Minister is no longer in full control of events washing around Downing Street will linger until the general election.