As William Hague promoted several Eurosceptics when he reshuffled his Shadow Cabinet yesterday, Mr Clarke said the Tories would not win the next general election if they became a "single issue party" because the turn-out would be much higher than the 23 per cent who voted last week.
In an interview with The Independent, his first since the Euro elections, Mr Clarke said: "It would be a terrible mistake if the first Conservative success for five years were thrown away by a rush of blood to the head."
Urging the Tory leader to withstand the "zealots" demanding a harder line on the single currency, he said: "William must not take the advice of hotheads who got carried away because 10 per cent of the population voted for them."
The former Chancellor appealed to Mr Hague to drop plans to expel Tory Europhiles who backed the Pro-Euro Conservative Party last week. He said he would be "very sad" if senior figures were thrown out for writing a letter to newspapers, which was "not a hanging offence".
Mr Clarke also had a stern warning for Tony Blair, who has angered pro- EU Tories by failing to "give a lead" on the single currency. He said that "a message of goodwill" from the Prime Minister would not be enough when the embryo Yes campaign for the euro is launched, and that he should be on the platform. "The behaviour of the Labour Party has made me more wary of speaking out when it won't," he said.
Writing in The Independent today, Lord Howe of Aberavon, the former Tory Foreign Secretary, warned Mr Blair that the pro-European case "cannot succeed by default". He told Mr Hague that last week's Tory campaign "did not enthuse the millions of uncommitted voters, whom we need to convince".
Yesterday Mr Hague delighted the Eurosceptics by tilting the balance of the Shadow Cabinet in their direction in his wide-ranging reshuffle. Buoyed by the European election, Mr Hague intends to defy Mr Clarke by making the single currency a central issue at the general election.
In his shake-up, Mr Hague sought to draw a line under the Major era by bringing in four new faces and sacking Peter Lilley, the party's deputy leader. He promoted Ann Widdecombe to the key post of shadow Home Secretary.
Clarke interview, reshuffle details, page 9;
Leading article, Review, page 3; Geoffrey Howe, Review, page 4Reuse content