The challenge came after Nadir, the bankrupt former chairman of the Polly Peck empire, accused the Conservative Party of mounting a 'deliberate disinformation campaign' to try to discredit him.
Speaking on BBC radio, Mr Heseltine, President of the Board of Trade, told Nadir to publish whatever information he has or shut up.
Nadir has told journalists in Turkish northern Cyprus that he has revelations that would provoke a Watergate-scale scandal in the British government and that he has tapes proving the ministers and Tory MPs colluded to destroy his business.
But Mr Heseltine was contemptuous of the threat. He said: 'Don't let's get involved in allegations. Publish it. Stop smears. Publish what you believe to be evidence.'
John Smith, the Labour leader, yesterday called on the Conservative Party to end the practice of inviting companies to make loans to it instead of payments which must be declared in their accounts.
Mr Smith's intervention came after a disclosure in the Independent of a Tory Central Office memorandum detailing a new scheme to enable companies to make payments without telling shareholders. Central Office said the memo was withdrawn soon after it had been drawn up and no company had acted upon it.
The Independent disclosed yesterday that Richard Ryder, Chief Whip, was once incorrectly described as a 'political consultant' to Christopher Morgan, who now acts for Nadir.
Mr Ryder said that at no time did he have a commercial or professional relationship with the consultant, and that the listing in a professional
year book was made without his knowledge. He has said that he never attended any commercial meetings for Mr Morgan or acted on his behalf.