MICHAEL HESELTINE last night launched an astonishing surprise attack on William Hague just hours after the Tory leader stunned Westminster by reopening his party's civil war over Europe.

The former deputy prime minister's outburst followed a keynote speech by Mr Hague in Paris, in which he warned the single currency was driving Europe dangerously close to political union.

Mr Heseltine joined forces with his pro-Europe ally, the former Chancellor Kenneth Clarke, to warn that increased Tory hostility to Europe could make the party unelectable.

Mr Clarke, who with Mr Heseltine, remains poised to lead a break-away pro-European wing of the Conservatives, warned: ''If the party goes off to the right, into Euro-scepticism, we will be unelectable.''

For his part, Mr Heseltine said Mr Hague's outspoken criticism of monetary union would marginalise Britain and the Tory party. He said: ''He is in danger of losing a very important part of the Conservative party - the centre ground - and you can't win unless you come from the centre ground.''

And in a comparison that will outrage Tory Euro-sceptics, Mr Heseltine declared: ''Mr Hague's language is more extreme even than that Mrs Thatcher used.''

Mr Hague's speech, seen as his most Euro-critical to date, shattered the calm on an issue that split the party and contributed to its landslide defeat last year.

It risked widening the gulf between the pro and anti-Europe wings of his party, and confirmed his decision to oppose the Government's decision to commit Britain in principle to joining Economic and Monetary Union (Emu).

Last autumn, Mr Hague changed Tory policy to rule out British membership of the single currency for the lifetime of this Parliament and the next. But with momentum in the City and at Westminster beginning to build behind British membership, the Tories could be left politically marginalised.

Speaking to the INSEAD business school at Fontainebleau outside Paris, where he was once a student, Mr Hague said the launch of the euro on January 1, 1999, would ''create as many problems as it solves'', leading to an ''increasingly centralised Europe''.

He said: ''I therefore believe that Europe should not press on towards an unacceptable degree of political union just to make the single currency succeed. I fear that a single currency could push us beyond the limits to Union.

''The single currency is irreversible. One could find oneself trapped in the economic equivalent of a burning building with no exits.''

Mr Hague peppered his speech with repeated references to the ''danger'' posed by the euro.