Mr Major knows Sir Michael well and was genuinely upset. But it will not have escaped his notice that his departure because of a "past indiscretion" in his private life ended one of the most extraordinary weeks of any election campaign. Sir Michael's was the third resignation of a Tory politician in five days. Worse, for the Conservatives, at least three other MPs are under a cloud of either a sexual or a financial nature.
Sex scandals play a disproportionately important part in British political life. The striking thing about the two that have rocked the Tories this week is the relative insignificance of those involved. Sir Michael is an important figure in Scotland and had hoped to become an MP in this election. But he is hardly a titan on the national stage.
The other case involves Piers Merchant, MP for Beckenham, who is alleged to have had an affair with a 17-year-old nightclub hostess. The MP, who denies the charges, holds the most junior of government roles - parliamentary private secretary. Neither man is the biggest scalp a predatory tabloid could wish for.
Yet their stories broke in a week in which Tim Smith, a cash-for-questions protagonist, finally bowed to pressure and stood down. Meanwhile, north of the border, Allan Stewart, a former minister, stood aside as well after admitting to having a relationship with a married woman while undergoing treatment for alcoholism. That unhappy saga took a final twist when Mr Stewart was admitted to hospital suffering a nervous breakdown.
That politicians should be hounded about their private life is deprecated by many from all parties. As one senior Tory put it: "If you needed an emergency operation and, as you were rushed to the operating theatre, somebody said to you 'Look, you do realise that the surgeon is an adulterer, do you still want to go ahead?', I think I know what your reaction would be."
Labour has been careful not to seize publicly on the sex allegations. But the revelations have added distractions to a campaign which has failed to focus on policies for more than two days at a stretch. One Tory strategist observed: "Every day when newspapers are full of sleaze stories is a day they are not full of other, more positive stories for us." Another added: "We clearly have some cleaning-up to do."
In practical terms that means getting "sleaze" out of the headlines. Central Office's target number one is Mr Merchant. In his letter to Sir Michael yesterday Mr Major went out of his way to praise him for quitting "so speedily and in a courageous and honourable manner". There can be no clearer code for offending MPs. Since the disastrous days of back to basics, the Tories have operated a drill under which those in government hit by scandal quit their posts quickly to get adverse media reaction out of the way. But while those on the government payroll can be easily thrown aboard, removing MPs from their livelihood is more complex.
Constituency parties guard their rights to appoint and de-select MPs jealously and, unlike the Labour Party, the Tories have little power to force their will on recalcitrant activists. Even pressure to bring a meeting of Mr Merchant's Beckenham party executive, planned for Tuesday, forward to yesterday were rebuffed. The local party is insisting on holding the meeting to decide their MP's fate on the eve of the Tory party's manifesto launch. Not what most would call ideal news management.
If the MP stands down he would be giving up one of the Conservatives' safest seats and saying goodbye to his career and only obvious source of income; a punishment which many feel out of proportion to any crime committed. But even if the leadership secures Mr Merchant's departure, that may only focus attention again on the other, more serious sleaze allegations against Neil Hamilton, the MP for Tatton, and Michael Brown, the MP for Cleethorpes. Both men admit taking money from the lobbyist Ian Greer without declaring it to the parliamentary authorities. After all, if an MP is unsuited to stand because of allegations of an affair, how can those charged with the more serious offences possibly survive?
Here again, many senior Tories wish Mr Hamilton would do the decent thing, but Conservative Central Office has stepped more carefully. Mr Hamilton, a linchpin of the right-wing No Turning Back group has powerful allies on the right of the party, including Michael Portillo, Secretary of State for Defence.
Although he has admitted a second stay at the Ritz in Paris and to claiming a free airline ticket as a business expense, Mr Hamilton argues that he had not been able to put his case, and that the Downey report - delayed because John Major prorogued Parl- iament early - will exonerate him. The MP has been careful to keep his constituency association well briefed on his case.
Labour yesterday was seeking to exploit cracks in the Tory association by announcing that its candidate in Tatton would stand down in favour of an all-party "anti-corruption" campaign.
In any event, media attention on Mr Hamilton and Mr Brown will continue until the two men's adoption meetings have taken place, giving at least another week of "sleaze" headlines.
While in one sense this is a gift for Labour, in private even the Opposition is starting to be alarmed at the turn the general election is taking. The danger is that politicians are tarred with the same sleazy brush, fuelling cynicism among the electorate. One Labour source said last week: "We might win, but we are already asking at what price?" Some even think that there might be a sympathy vote for Mr Major. "The great British public," said one, "will not allow Major to be humiliated."
Some Labour strategists agree with the Tory verdict that this is the "political equivalent of mud-wrestling". Paddy Ashdown, the Liberal Democrat leader, may have gained by staying outside the fray even if, as one Labour source put it "he does sound like the vicar trying to lead the youth club into action".
Significantly, Tony Blair has decreed that Labour's remaining advertising blitz will concentrate on positive, rather than negative messages. That is because of a feeling, picked up in the Wirral by-election, that the voters were reacting badly to the party-political slanging match. Labour's poster featuring a two-faced John Major, telling different stories on tax will be replaced by a more positive image, to be launched this week, stressing that Labour can make Britain better.
On the Conservative side loyal Tories insist the media obsession with sleaze is not shared by the public. But more admit to the frustration felt at the loss of momentum after landing punches on Labour when it failed to clear its lines on the detail of its policy to allow union recognition.
Strategists point out that because of the length of the campaign, the media will be forced to move to more substantive issues in the final, crucial three weeks. But the Tories have a mountain to climb simply to regain any control of the agenda by which they will be judged.
As one Labour Party official put it: "We have this incredible political machine, but so far it's a bit like Scotland versus Estonia the first time round - the other side haven't turned up."