Kenneth Clarke has branded David Cameron's proposals for a British Bill of Rights "xenophobic" and "anti-foreigner".
In the fiercest challenge yet to the new Tory leader the former chancellor warned that Mr Cameron would "struggle" to win support from lawyers for his plan to replace the Human Rights Act.
Mr Cameron's aides immediately hit back, dismissing Mr Clarke's comments as ludicrous.
In a speech on Monday Mr Cameron said the Act was "practically an invitation for terrorists and would-be terrorists to come to Britain".
He declared: "I believe it is wrong to undermine public safety, and indeed public confidence in the concept of human rights, by allowing highly dangerous criminals and terrorists to trump the rights of the people of Britain to live in security and peace."
Mr Clarke, chairman of the Conservatives' democracy task force, told The Daily Telegraph yesterday that Mr Cameron's plan was "xenophobic and legal nonsense". He added in an interview on the the BBC's Daily Politics show "His remarks were anti-foreign. I think the convention on human rights - I haven't looked up the history - was written by a conservative lawyer after the war."
Mr Clarke said: "In these home affairs things I think occasionally it's the duty of politicians on both sides to turn round to the tabloids and right-wing newspapers and say, 'You have your facts wrong and you're whipping up facts which are inaccurate'."
The former Tory leadership contender, who was defeated by Mr Cameron in a ballot of MPs, said he had not been consulted about the proposals for a new Bill of Rights. He said: "I think he is going to have a separate task force on the Bill of Rights. He never mentioned to me he was going to make these remarks. He is going out there to try and find some lawyers who agree with him, which I think is will be a struggle myself."
Mr Clarke, one of the strongest pro-European voices in the Tory party, has clashed with Mr Cameron over his plan to pull Conservative MEPs out of the European Parliament's main centre-right group, the European People's Party.
Mr Clarke's comments came as Mr Cameron's plan to scrap the Human Rights Act provoked a strong backlash from lawyers and civil rights campaigners, who pointed to a string of people who had benefited since the legislation came into force six years ago.
Mr Cameron was heavily criticised by ministers and human rights activists, despite making it clear that he planned to keep Britain in the European Convention on Human Rights.
A spokesman for Mr Cameron said last night: "Ken is Ken. He has a very colourful way of expressing himself. We totally reject the comments he made.
"It's ludicrous to suggest that a Bill of Rights is somehow anti-foreigner or xenophobic. This issue is outside the remit of Mr Clarke's task force which is why there is no need to consult him on it."
The spokesman insisted that Mr Cameron was "relaxed" about Mr Clarke's comments.
He said: "David does not believe in making examples of people for the sake of it. He will judge him on the work that he produces."Reuse content