Max Clifford, who acted as a go-between in the exposure in a Sunday newspaper of the affair with Sir Peter Harding, Air Vice-Marshall, said on BBC radio: 'She feared for her life. She was meeting Sir Peter. There were no guards around. All kinds of things were going on.'
Speaking on the Moral Maze programme, Mr Clifford said that Lady Buck, the divorced wife of the former Tory MP Sir Anthony Buck, believed her life had been threatened. A Sunday newspaper which has bought her story will publish the details at the weekend, he said.
He did not say from whom the threat came. But senior defence sources discounted the claims last night. 'It is going from the gutter to fantasy land,' a ministerial source said.
The source also rejected a report that MI5 had intercepted and read love letters from Sir Peter to Lady Buck. The report raised questions among Tory MPs about why MI5 had not warned ministers of the affair which led to Sir Peter's resignation at the weekend, when the details were published.
Senior civil servants at the Ministry of Defence assured ministers that there had been no interception by MI5 of letters by Sir Peter.
It was also confirmed that Malcolm Rifkind, the Secretary of State for Defence, had no knowledge of the affair until he was telephoned by Sir Peter last week and told the reports were likely to appear.
David Clark, the Labour spokesman on defence, welcomed the inquiry, which he had demanded in a letter to Mr Rifkind. Dr Clark said: 'I obviously was concerned because this man knew all our military secrets and those of our allies.
'I was concerned the MoD might not institute an inquiry. But I am reassured now they have done so, and we will just have to wait and see what the inquiry comes up with, to see if there has been any transgression of security.'
In a letter to Mr Clark, Mr Rifkind said: 'I have already put in hand appropriate inquiries to establish whether security may have been compromised.
'When I have the conclusions of that work, I shall decide what further steps, if any, might be appropriate.'