The former Deputy Prime Minister said the party had to unite if it wanted a chance of getting back into power. Otherwise, it faced the prospect of Labour's fate when it lost office to Margaret Thatcher - 18 years in opposition.
"We have got to be united," he told BBC radio's The World this Weekend, "and that does mean that people have got to want to come together to seek the point, the fulcrum, from which we can operate."
But he then went out of his way to respond to a Sunday newspaper report that Baroness Thatcher was urging right-wing candidates to ensure that neither Mr Clarke nor William Hague win this month's leadership contest - something denied yesterday by Peter Lilley, the former social security secretary.
Mr Heseltine said: "I hope the party is not going to say, `Well, Ken is a long way ahead on the first ballot, now we've got to find a way of stopping him'. That, frankly, does seem a pretty poor way of thinking about it - `We just want to stop Ken Clarke as a candidate'. Frankly, that is not the way to win popular esteem."
Mr Heseltine, Douglas Hurd, the former Foreign Secretary, and Sir Norman Fowler, the former party chairman, are all featured on a Clarke campaign video being sent out to about 1,000 key party figures this week.
Others contenders maintained their gruelling round of meetings and speeches yesterday, with Mr Lilley addressing a London rally at which he told activists that unity was "paramount", and he was the man to deliver it. "I don't just preach unity," he said, "I have been practising it." He said he had driven through 12 welfare reform Bills with no rebellions, splits or dissenting Tory votes.
"I did it by knitting together all the strands of opinion in the party. That is what we need to do now across all the strands of opinion in the party."
But the spectre of Europe was again raised yesterday by Michael Howard, who told activists at Duxford, Cambridgeshire, that he wanted a new deal in Europe, with individual states allowed to "repatriate" many of the powers that had been ceded to Brussels control.
A press release issued by his campaign said: "Beyond their core commitment to the single market, EU members should be allowed to pick and choose which initiatives to join.
"This could allow for the repatriation of powers not related to free trade. While it would be for future Parliaments to decide which powers might be retrieved, agriculture, fisheries and environmental regulations are all possible candidates."
Interviewed on BBC television's On the Record, Mr Hague said his recent reference to the "constantly shifting fudge" of the last government had not been an attack on John Major, but a reference to Cabinet members' divergence from agreed Cabinet lines. That had given an impression of a lack of clarity on Europe.Reuse content