I'm appalled by the total refusal to engage in any satisfactory negotiations

Kenneth Clarke MP

He said: "It's important we don't give an excuse to the Russians or anybody else to start breaking other agreements that might lead for example to the proliferation of nuclear weapons.

"The problem has to be addressed but I'm a cautious supporter.

"I don't want to run ahead of the Americans.

"If I was asked for my advice I would advise them to proceed with considerable caution."

He raised concerns over the US Republican leadership's resistance in the face of international pressure on the Kyoto Protocol.

Former era

He said: "Arguments about the details of the Kyoto convention I can understand, not least because the President has to sell any deal to the American congress, but I'm afraid I'm appalled by the total refusal to engage in any satisfactory negotiations.

"The Kyoto convention is extremely important and it's seriously weakened by the absence of the government of the world's major economy.

"These are early days for the Bush administration.

George W Bush: no change on Kyoto

"He was elected on an `American first' policy but I still hope he can reassure us he can square that with America's international obligations at the same time."

He went on to comment on Mr Duncan Smith, widely regarded as the "Thatcherite" candidate, as someone who represented "another era".

Mr Clarke said: "I think that the perception of the Conservative Party is it got left behind by events and with the greatest respect to my colleague Iain Duncan Smith, he is asking us to move far further to the right of William Hague and represents a throwback to another era ... I don't believe in going back to another era."