Uphill EU battle for Blair

By Mark Mardell BBC chief political correspondent

If you listen to one side, the whole of British history is at stake. Take notice of the other, and it's just a modest tidying up of the rules of a club.

A referendum defeat for Blair (r) could see Gordon Brown become PM

The ferocity of the debate in Britain will swirl around this gulf between the two different interpretations of what the EU Constitution will mean.

Neither side expects a referendum until 2006 and neither side wants to start campaigning too early.

Although the campaigns are independent of political parties and MPs will not be bound by their party's preference, it is obvious that the main political impetus for a Yes vote will come from Labour, the main force for a No from the Conservatives.

Neither side wants to expend its energy ahead of a general election campaign, expected in May next year.

Yet it promises to be a far more interesting campaign than the election, which most people expect Labour to win with a slightly reduced majority.

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The EU constitution

But the outcome of a referendum campaign is both uncertain and important. There will be many who will argue that Tony Blair cannot campaign for a "yes" vote, lose it, and then continue as prime minister.

There are many in the Labour Party who hope that he will lead his cause to a glorious and heroic defeat and then choose to pack in and hand over to Chancellor of the Exchequer Gordon Brown.

'Slippery slope'

The referendum could be a momentous crux for British politics for reasons entirely unconnected to Europe. And this is not fanciful speculation - as things stand it is likely that Mr Blair will be defeated.

The No campaign know they operate in a world where the distrust of politicians is strong

The No campaign is well organised and run by youngish backroom boys who you will never see on the TV. They are the same people who ran the "Vote 2004" to persuade the government to hold a referendum. They may never have expected to succeed in that cause, but they did.

They are the same people who were involved in the "No to the euro" campaign, which they also judge a success because the government has not taken Britain into the single European currency, and does not look as if it is about to.

In this campaign their argument will be that the constitution is unnecessary, that only countries have constitutions and this is another side down the slippery slope.

Most Conservatives are expected to back the No campaign

They will have the Conservative Party, the UK Independence Party and the Greens on their side. But while in the heat of battle these party leaders will not go unquoted and unheard do not expect them to be the front men and women.

The No campaign know they operate in a world where the distrust of politicians is strong. Indeed, part of their argument has to be that while politicians say the constitution is one thing, it is in fact another.

So they are currently courting rock stars, celebrity chefs and TV personalities. But they know their biggest ally is likely to be the Eurosceptic press, the Sun newspaper in particular, which will shout the argument with little subtlety but great impact.

Groundwork missing

The Yes campaign is much less well organised, and indeed rather dispirited by the Labour government's reluctance to blow the starting whistle. Indeed, this has dogged the pro-European campaigners in all their guises.

Mr Blair is good at pulling rabbits out of hats, but he will need all his conjuring skills to win this one

The government, entirely reasonably, has never wanted to promote an unpopular cause before it is absolutely necessary. This means, Yes campaigners feel, that the groundwork has never been done.

It certainly has not been decided who will front the campaign. But it is inevitable that TV, radio and the press will decide that the job goes to Tony Blair.

When the government decides to hold a referendum and is urging the country to vote Yes then it is a foregone conclusion that the prime minister will be seen as leading the campaign.

At the moment only the truly committed are engaged, while the opinion polls indicate a majority are against the constitution. Mr Blair is good at pulling rabbits out of hats, but he will need all his conjuring skills to win this one.