The British Conservative leader, Mr William Hague, has raised the stakes in the debate over the single currency by challenging the prime minister, Mr Tony Blair, to face up to the euro's troubled birth and dump his plans to prepare Britain for ditching the pound.

Mr Hague said the government had to face the "hard facts" of a devaluing currency and abandon the National Changeover Plan, launched in February to prepare Britain for joining the euro.

But Foreign Secretary Mr Robin Cook condemned the call to scrap the changeover plan as "deeply irresponsible". He said without the plan there could be no real debate ahead of the promised referendum on joining the euro.

The British government has pledged to scrap the pound if five economic tests are met and the public back the move in a referendum.

In the meantime, Mr Blair has ordered government departments to start spending tens of millions of pounds on preparing to work in euros and has asked businesses to do the same.

But Mr Hague said the move was wrong ahead of any vote by the people in favour of the euro.

And it was becoming increasingly clear that not only was the euro in a downward spiral but the economies of its member-states - which were supposed to converge - were increasingly out of step.

Shadow Chancellor Mr Francis Maude accused the Government of being "in denial" over the euro's problems.

"So dogmatically are they committed to joining that they have shut their eyes to the facts," he added.