The lurid details of his affair with Antonia de Sancha, spread over the tabloids, wounded him seriously but not fatally.
It was the revelation during Mona Bauwens's libel action that the then Minister for the Arts had accepted the gift of air tickets for his family from Mrs Bauwens for the month-long family holiday to which Mr Mellor apparently contributed little that finished him.
Whitehall's ministerial rule book Questions of Procedure for Ministers is crystal clear. It is, the procedure states, 'a well-established and recognised rule that no minister . . . should accept gifts, hospitality or services from anyone which would, or might appear, to place him or her under an obligation.
'The same principle applies if gifts, etc are offered to a member of their family.' The sums involved may not have been enormous. In normal times the issue might have been buried. Mr Mellor might have escaped with a reprimand. But coming on top of Conservative MPs' doubts about the judgement he displayed in the wake of the revelations about his affair it drained Conservative backbench support. Not even total loyalty from the Prime Minister could save him.
When the story of Mr Mellor's affair first broke in July, John Major's judgement that Mr Mellor should stay seemed tenable. Enough people at Westminster live in the same glass house for a brief affair with no security implications to appear no reason to end a political career.
It was Mr Mellor's subsequent behaviour - and further revelations about the unemployed 31- year-old actress in whose one- bedroom flat Mr Mellor apparently romped to exhaustion on a mattress on the floor - that raised the first serious doubts.
On the Monday after the Sunday newspapers broke the story, Mr Mellor's appeal to be left in peace for the sake of his children backfired among Conservative MPs who felt he should have thought of that first. By the Wednesday, the Daily Mirror had disclosed that his wife Judith learnt of the liaison, over which the News of the World and the People had been pursuing him for a fortnight, not from Mr Mellor, but in two phone calls from the family lawyers.
And the next day the Mirror and others carried interviews with Mrs Mellor's 75-year-old parents saying he had telephoned to tell them to stop talking to the media or 'you'll never see your grandchildren again'.
The picture of an arrogant, uncaring and bullying minister did nothing for Mr Mellor while to cap it all the Sun had seven lurid colour pictures showing that Ms de Sancha had mixed her desire to play Shakespeare with a role as a one-legged prostitute simulating sex with a pizza delivery man in a film made last year.
The Daily Mail, which earlier in the week had argued that the 'brilliant, if bumptious' politician should remain, changed its tune.
Mr Mellor's position was 'no longer tenable', the Mail said, approvingly quoting his father-in- law, who had said: 'If anyone breaks the most sacred vows he ever makes in his life (of matrimony), he might break a few other vows, like Privy Councillor vows.'
The Mail summed up a growing backbench feeling that 'the more that has become known . . . the more flawed his judgement is seen to be'.
It put a team of reporters on Mr Mellor's financial affairs for six weeks before producing a report on his links with the property developer Elliott Bernerd, who provided a flat where Mr Mellor at times met Ms de Sancha, and loaned him a car.
Their efforts failed to demonstrate any impropriety. But the Mail's renewed assult coincided with 'friends' of Ms de Sancha producing yet spicier accounts of his liaison - including claims that Mr Mellor appeared from the bathroom in Chelsea strip before leaping on his lover.
With 'friends' like that, Mr Mellor hardly appeared in need of any more. But Mrs Bauwens's revelation on the first day of her libel action against the People that she had paid for the Mellor family's travel for their stay with her in a luxury Marbella villa she had rented proved the final straw.
His acceptance of the gift, his failure to see that it might 'appear' to place him under an obligation, and his failure to refer it up to Margaret Thatcher for approval, all left increasing numbers of backbench colleagues believing he had to go. Questions of Procedure for Ministers states clearly 'any minister in doubt or difficulty' over whether a gift might appear to create an obligation 'should seek the Prime Minister's guidance'. Mr Mellor's resignation marks the end of a rumbustious career for the 43-year-old MP, who won his Putney seat in 1979.
Within two years he was the first of his intake to reach ministerial office as the junior at energy and in 1983 was moved to the Home Office as minister in charge of drugs and broadcasting, where his rare talent for both publicity and self-publicity became evident. Critics said the whirl of publicity disguised a lack of real action.
He was promoted to Minister of State at the Home Office, the first of five Minister of State posts which left both friends and enemies believing he was destined always to move sideways and never up to the Cabinet.
At the Foreign Office, he caused an international incident by accusing an Israeli officer on camera of inhumanity to Palestinian Arabs on the Gaza strip.
The combative style and a supreme self-confidence that his detractors saw only as arrogance, won him mixed reviews from civil servants. They admired his intelligence and speed of thought but often disliked his personal style.