The executive committee of the 1922 Committee - representing Tory backbenchers - is expected to make it clear today that Mr Mellor should go. That would seal his fate.
Earlier, Mr Mellor had mounted a robust counter-attack. The Secretary of State for National Heritage strode into a City guild hall in London packed with journalists, including some of the editors of newspapers calling for his resignation, and said: 'What do you want to know?'
Mr Mellor used a charity event to answer for the first time detailed charges that have led to the calls for his resignation.
'I've had the feeling there are some who would like to hound me out of office. I think there is at least one newspaper which is not used to having its editorials ignored by Conservative prime ministers and is determined to hound me from office.
'I accept that is a judgement for others. I believe there is a reasonable and rational explanation to everything, beyond the initial business with Antonia (de Sancha) which I have to accept. Those who think that ministers should not survive if they have an affair . . . well, they've got me.'
He said he was willing to resign if he was an embarrassment to the Government, but, sipping from a glass of red wine and surrounded by reporters, Mr Mellor said he had not broken any ministerial rules on the acceptance of gifts.
Mr Mellor continued his counterattack during a live interview on News at Ten, when he gave a vigorous and fluent defence of his conduct. He then moved to BBC 2's Newsnight studio, where he blamed his difficulties on 'four or five tabloid editors' and added: 'The crucial point is who decides who is a member of the British cabinet, the Prime Minister or the editor of the Daily Mail.'
His remarks came as details emerged that the minister enjoyed a second free foreign family holiday. This was at new year 1989/90 when the Mellors were in the Middle East as guests of Sheikh Zayed, the ruler of Abu Dhabi, who controlled the Bank of Credit and Commerce International which was shut down by banking authorities last July.
Mr Mellor was entertained on an island owned by Sheikh Zayed in the Persian Gulf. Another guest was Mona Bauwens, whose High Court libel case first focused attention on a free holiday she had provided for the Mellors at a villa in Marbella.
Mr Mellor's office told the Independent last week that the minister had gone to Abu Dhabi on an official visit. But last night it was confirmed that he had been invited 'in his private capacity'.
The disclosure could intensify the pressure for Mr Mellor to resign, but his office said the Foreign Office and the Home Office had both known about the visit.
Mr Mellor said last night: 'I had a series of meetings with (Sheikh Zayed) and with other senior ministers. It was known by the Foreign Office and approved by them.'
Bryan Gould, Labour's spokesman for National Heritage, wrote to the Prime Minister last night over allegations that Mr Mellor had asked the British embassy to sort out the plumbing at his Marbella villa. Mr Gould called for Mr Mellor's resignation.
Mr Mellor said that the water system had stopped working. Because none of the guests could speak Spanish, he telephoned the consulate for assistance. They gave him the name of a water company and the matter was put right.
Despite Mr Mellor's spirited performances last night, one senior member of the 1922 committee said: 'His chances of surviving until the weekend are nil.
'If he had any sense, he would go before we meet. He is quite honestly now an embarrassment to the party and an embarrassment to John Major.'
The Prime Minister has stood by Mr Mellor when many expected him to be sacked. But Mr Major's loyalty has been stretched by the continuing revelations of Mr Mellor's acceptance of a pounds 10,000 holiday with his family at a luxury Marbella villa with Mrs Bauwens, daughter of a leading member of the Palestine Liberation Organisation.
'Interfering' Mellor, page 2
Leading article, page 28