Controversy may be seen as watershed: Allegations of a minister's affair with an actress focus attention on press regulation and electronic eavesdropping

IF DAVID Mellor survives the controversy over his alleged affair with an actress, it could mark a watershed in the standards expected of ministers in their private lives.

Cabinet ministers yesterday privately rallied round in support of Mr Mellor, but British ministers have invariably had to resign over sex scandals in the past.

The most notorious sex scandal of the century occurred during the sixties.

John Profumo, the Secretary of State for War, resigned in 1963 over his affair with Christine Keeler. Although there were allegations that secrets may have been passed to a Soviet agent, he resigned because he lied to the Commons by denying the liaison.

Ten years later, Lord Lambton resigned as the defence minister responsible for the Royal Air Force after being photographed in bed with two call girls. Earl Jellicoe, then Leader of the House of Lords, resigned within a few days over the vice-ring scandal.

The Profumo affair destabilised the government, Harold Macmillan resigned in ill-health within the year and the Tories were defeated at the next election. The Jellicoe-Lambton scandal was followed a year later by the defeat of the Heath government.

Prime ministers have tended to prefer to play down sex scandals, or cover them up, rather than risk the political dangers of disclosure. John Major's message of support may be seen in the same light.

That was Margaret Thatcher's reaction when Cecil Parkinson offered to resign after admitting his affair with Sarah Keays, his former Commons secretary, who was pregnant by him. Mrs Thatcher - now Baroness Thatcher - said that the question of his resignation 'does not and will not arise'. Her pragmatic view of private life and public morality was not shared by the party. It was appalled. There was no allegation of a conflict of interests, apart from the charge of hypocrisy against a party chairman and secretary of state for trade and industry who had helped to lead the Tories to victory as the party of the family.

There are no rules on sexual morals laid down in the Cabinet document on ministerial conduct issued under the Prime Minister's open government edict. Its advice is directed to a conflict of interests on investments, rather than liaisons.

John MacGregor, the Secretary of State for Transport, entertained European transport ministers last week at a dinner by recalling how Lady Caroline Lamb had surprised guests at the same table at a birthday banquet for Lord Melbourne, later to become prime minister, by leaping naked out of a soup tureen.

Such behaviour would have provoked moral outrage in this century. But times are changing.