Eric Chalker, a member of the Conservative Party's board of finance for four years until 1993, said: "It is now time to do the decent thing, and hand the money back."
He echoed the words of another former Tory treasurer, Lord McAlpine, who last week compared taking Mr Nadir's donations to receiving a stolen car, and said the money should be returned for distribution among the creditors of his failed company, Polly Peck International.
And he said of the money - believed to be up to pounds 50,000 - given to the party by Mr Tancic, whose companies were on a US sanctions blacklist: "It is not a donation which Central Office should have accepted."
The Independent on Sunday last week revealed that three years ago Conservative Central Office received a confidential report from the accountants Touche Ross, Polly Peck's administrators, which said that pounds 365,000 out of pounds 440,000 given to the party by Mr Nadir came from stolen money. The "highly sensitive" Touche Ross report stated: "The evidence we have to date shows that a large proportion of the pounds 440,000 donations made to the Conservative Party formed part of Mr Nadir's fraud and/or breach of fiduciary duty and/or breach of trust and/or misfeasance as a director."
Yesterday The Independent disclosed that Mr Tancic, 49, had made a donation which was accepted by the party, even though his companies, Metta Trading Ltd and Metalchem International Ltd, were on the US Treasury sanctions blacklist. The newspaper also established that a former director of Metta Trading was Jovan Zebic, sometime Serbian finance minister and now deputy prime minister, who was credited with raiding Yugoslav reserves to fund the Serbian war effort in Bosnia.
Mr Chalker, well-known for pressing for greater accountability within the party, said: "At best, the donations are tainted. But it seems to me that the case is much stronger than that. It's a personal responsibility of the Prime Minister."
The former husband of Baroness Chalker, the overseas aid minister, Mr Chalker also last night called on Mr Major to identify donors making large gifts to the Conservative Party and to ban all political donations from foreign sources.
He said: "It is totally unacceptable that a political party can accept six-figure donations and keep that secret. I just do not believe one can be sure that donations on that scale are given for wholly altruistic reasons.
"It is utterly wrong for a political party, certainly in a mature democracy like the United Kingdom, to take money from people abroad who have no part in our elections."
Yesterday Robin Cook, the Shadow Foreign Secretary, said that the Tory chairman, Brian Mawhinney, had written to him indicating that the Conservatives would not return the Nadir donations.
"He said they believed that the money was 'legitimately received'," said Mr Cook. "Initially, their criteria for accepting money was that it had to have been 'legitimately made'.
"They seem to be moving the goalposts, and the sad truth is that it now seems the Tories will sink so low as to be receivers of stolen goods."
He too called upon the Conservatives to return Mr Tancic's donation. He said: "I will be writing to Mr Mawhinney asking whether he was aware that these companies were on the blacklist and inviting him to give the money back. If the company was blacklisted, they should not have accepted the money.
"The presence of the Serbian finance minister in the company shows that it had links with the very top of the Serbian government. The Americans must have found it very odd that the Conservative government was willing to accept a donation from a company with which the US government would not even trade."