'Tell us euro cost' - Hague

William Hague wants to keep campaigning on Europe

Conservative leader William Hague has challenged Tony Blair to reveal the true cost of joining the euro.

The Tories sought to keep Europe top of the election agenda with a claim that Britain would end up paying £36bn - or a new Millennium Dome every month for three years - to switch to the single currency.

He is setting out the real agenda and it shows we need a government that will be in Europe but not run by Europe

William Hague on Lionel Jospin

They also seized on a speech by French Prime Minister Lionel Jospin, saying Tony Blair wanted to sign up to his ideal of the European Union's future.

But Labour accused Mr Hague of being obsessed by Europe and dismissed the Tory claims as "nonsense" while the Liberal Democrats said they were a "joke".

The Bank Holiday campaign theme was set by Mr Jospin's keynote speech in Paris.

He rejected German proposals for a more federal Europe, saying he preferred a Europe of independent nation states.

But he went on to call for the harmonisation of business taxes, an "economic government", a European constitution and a "social treaty".

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The Tories said the French premier had set out the "the real agenda", and also accused Labour of planning to rig any referendum on the euro.

And, using a City accountancy firm estimate, the Conservatives said joining the single currency could cost Britain £36bn - £1,500 per household, or the equivalent of 36 new Millennium Domes.

'Loaded' question

Mr Hague said: "We are challenging Mr Blair today to say what the costs of joining the euro would be and to say what the question would be.

"If they are not prepared to say what the question would be in a referendum, then we know that they are planning to give people a loaded question."

As Mr Jospin was a "close ally" of Mr Blair and Chancellor Gordon Brown, his speech showed "we need a government that will be in Europe but not run by Europe", the Tory leader said.

Mr Blair took part in a Bank Holiday kick-about

Later, shadow foreign secretary Francis Maude conceded the £36bn figure "may not be the right figure" but said if the government had a better one "let it share it with the public".

The prime minister ridiculed the Conservative claims, calling them "the usual Tory nonsense".

Speaking while campaigning at a fete in his Sedgefield constituency, he said Mr Hague "seems absolutely obsessed" about the euro.

"But I will tell you what I'm obsessed about. I'm obsessed about keeping our economy strong, our mortgages low, the number of jobs high, and then putting schools and hospitals first so that we get in the investment we need."

Mr Blair, who was with his teenage son Euan, took part in a football kick-about - although the bank holiday mood was overshadowed by barracking from keep-the-pound and fuel duty protesters.

Charles Kennedy says the Tories have given the country a "belly laugh"

Liberal Democrat leader Charles Kennedy said the Tory claims were a joke.

"I don't think that people have such short memories that the Conservatives are liable to hoodwink anyone into believing the figures they are coming forward with at the moment," he said.

But the figure was £36bn was defended by Maurice Fitzpatrick, head of economics at accountants Chantrey Vallacott, who made the calculation.

He told the BBC: "We broke the economy down into various sectors and we tried to use wherever possible published research, generally by other firms of accountants... to produce what we felt was a realistic global figure.

"If anything, we have erred on the conservative, ie low, side."

In other campaigning on Monday, Labour announced plans for a new National Lottery fund to target £150m at some of the country's most deprived areas.

The Tories dismissed it as "a bit of spin".