Tony Blair owes William Hague a debt of gratitude. The prime minister says he can win a post-election referendum to take sterling into the single European currency. Mr Hague is doing his level best to help him. Never before has the leader of an opposition party so eagerly anticipated defeat.

Mr Hague's decision to run the last lap of his campaign attacking Europe in general, and the euro in particular, was always going to smack of desperation. At precisely the same moment in 1997, John Major offered his apocalyptic vision: the very Union of the United Kingdom was in peril. If Labour won, devolution would leave the UK "a divided, weakened pawn in a federal Europe".

The voters were unmoved. Mr Blair was duly elected, Scotland got its parliament, Wales its assembly and life went on much as before. So catastrophic were Labour's constitutional reforms that they have gone almost unmentioned during this campaign - not least by Mr Major's successor.

History is repeating itself. The "Save the Pound" countdown defies the intelligence of the electorate. More than two-thirds are opposed, at present, to joining the single currency. But most are equally sceptical about claims that Britain would be cast into servitude. France is still a proud nation. Germany governs itself And anyway, people can make themselves heard in the referendum. As in advertising, so in politics: messages must be credible in order to be effective.

That, though, is only part of the miscalculation. In his efforts to frighten the punters, Mr Hague has said the referendum is all-but lost even before it has been called. Mr Blair, he says, is "likely" to win, albeit because he will "rig the terms" of the plebiscite.

A vote for Labour is thus one to scrap the pound. If Mr Blair returns to 10 Downing Street on June 8, the game is up. This plays directly into the hands of the pro-euro camp. It wants to promote the feeling that participation in the single currency is inevitable. People might not much like the euro but, in the real world, there is not really much of a choice. The "Yes" campaign has put itself on the side of prosperity and jobs. Mr Hague has chosen to march in defence of a sovereign Westminster.

Another consequence is to strip off the bipartisan veneer of the "No" campaign. The pressure groups opposed to the single currency of course have the odd Labour politician on their letterheads. And Lord [David] Owen - remember the SDP? - is ever in search of a cause. But the anti-euro cause is now associated indelibly with the soon-to-be-defeated Mr Hague.

In this guise, the euro is only one among many manifestations of the Brussels tyranny. Britain, Mr Hague says, must renegotiate the basic terms of its European Union membership. If others demur, the only plausible sanction is withdrawal. The anti-euro cause becomes an anti-European one.

The opportunity here for Mr Blair is obvious enough. The euro debate can be framed as part of a much bigger decision about Britain's place in Europe. Should it swim in the mainstream or should it paddle alone in the waters around its own shores? That question was asked of the voters in 1975. The answer given then has not changed.

And yet Mr Hague knows he is going to lose the election and on June 8 Mr Blair will indeed return to Number 10. The Tory leader and his colleagues admit as much when they argue, even in advance of polling day, about the wording of the referendum question. Mr Blair, meanwhile, is assured that there is no longer a soul in the country who can feign surprise if he opts for an early plebiscite.

Mr Hague's rationale for this extraordinary approach has been that it will shore up support from his party's core constituency. The 25 or 30 per cent of the electorate who could never contemplate joining the single currency will turn out on general election day to back the Conservatives.

Perhaps such tactics will add a percentage point or two to his party's share of the vote. But that is as nothing against Mr Hague's strategic blunder.

In 10 days he will wake to find himself disowned not only by such eminent pro-European Conservatives as Kenneth Clarke, Chris Patten and Michael Heseltine, but also by many whose anti-euro cause he presumes to lead. Mr Hague might yet survive as leader of his party. The worse the election outcome, the less the likely competition for his job. I know one politician, anyway, who fervently hopes so - Tony Blair.