Michael Fallon is not John Profumo. Nor are the scandals now sweeping Westminster, which this week led to Fallon’s resignation as Secretary of State for Defence, yet as extraordinary as the convulsions which shook the Conservative Government in 1963 and led to Profumo’s resignation as Secretary of State for War.

But a comparison between this and previous scandals is still worth making. Every scandal which claims a scalp prompts the question, “Does this particular person deserve to be singled out for such severe punishment?”

Macaulay, in his review in 1831 of Thomas Moore’s Life of Lord Byron, denounced our national tendency to pick on individuals in this way:

“We know no spectacle so ridiculous as the British public in one of its periodical fits of morality … some unfortunate man, in no respect more depraved than hundreds whose offences have been treated with lenity, is singled out as an expiatory sacrifice … Our victim is ruined and heart-broken. And our virtue goes quietly to sleep for seven years more.”

Matthew Parris, at the start of his book on Great Parliamentary Scandals, makes the same point in a different way:

“Some who people these pages were badly wronged by reports, others destroyed by untruth or mere rumour. Many were hounded into ignominy by a press or public which had got its teeth into something which was culpable, got it all out of proportion, and simply would not let go. Some of the cruellest injustices you will find here arose not from media lies but from media half-truths: not from invention, but from too narrow a view of the facts.”

And yet the media’s eagerness to publish whatever discreditable material it can dig up is an essential check on power. Politics, one might say, is an unending battle between respectability and scandal; between ministers trying to demonstrate that they are perfectly virtuous, and a press which loves to show our masters are perfectly dreadful.

The Prime Minister’s role is to marshall the forces of respectability. One of his or her duties is to uphold, both in his or her own person and as leader of the Government, the standards of behaviour which command the support of respectable people.

That may sound, to some readers, like a glimpse of the obvious. But I confess it only occurred to me while writing a volume (which will appear next March) of brief lives of all 54 Prime Ministers from Sir Robert Walpole (in power 1721-42) to Theresa May.

Here are almost three centuries of attempted, and for long periods achieved, respectability. Only two of those 54 PMs (the Duke of Grafton, 1768-70, and Sir Anthony Eden, 1955-57) have got divorced (and neither of them, as it happens, was a great success as PM).

The press’s role is to unearth and prolong a good scandal, or series of scandals. It loves to expose as rank hypocrisy the claims made by the Prime Minister and the rest of the political class of respectability.

This task is highly enjoyable, and an excellent way of attracting readers. But not the least of its attractions is that it can also be presented as a noble endeavour.

“It is a moral issue”, as The Times headlined its celebrated editorial when the Profumo scandal was at its height in the summer of 1963:

“Eleven years of Conservative rule have brought the nation psychologically and spiritually to a low ebb… The Prime Minister and his colleagues can cling together and be still there a year hence. They will have to do more than that to justify themselves.”

Harold Macmillan resigned as Prime Minister in October 1963. The immediate cause was his health: he had prostate trouble which turned out to be less serious than at first thought.

But the Profumo scandal had already gravely weakened him, for it inflicted terrible damage on the reputation of him and his colleagues. Here was a farce involving a blonde, a brunette, a peer, a physiotherapist, a country house and its swimming pool, a Cabinet minister, a Soviet defence attaché and a supposed threat to national security.

The minister, Profumo, was foolish enough to deny in the Commons that he had slept with the brunette, Christine Keeler, who had also been enjoying the attentions of the attaché.

The blonde, Mandy Rice-Davis, when told in court that the peer, Lord Astor (whose son is Samantha Cameron’s stepfather) denied having slept with her, uttered the immortal words, “He would, wouldn’t he?”

The press revelled in the story, in June 1963 Profumo owned up to his lie and resigned, and Macmillan was assailed in the subsequent confidence debate by Nigel Birch, one of three ministers who had resigned from the Treasury in 1958, who quoted with deadly effect from Browning’s poem The Lost Leader:

“…let him never come back to us!

There would be doubt, hesitation and pain,

Forced praise on our part – the glimmer of twilight,

Never glad confident morning again!”

The Prime Minister looked old, out-of-touch (“I do not live among young people much myself” as he said at one point, while explaining why he thought a letter from Profumo to Keeler beginning “Darling” was harmless), and unduly inclined to place his trust in members of the upper classes.

May is perhaps by contrast quite well placed, as a woman, to show she understands the “rend in the fabric of patriarchy”, as Naomi Wolf calls the fallout from the Weinstein revelations.

But one does not envy the Prime Minister the task of distinguishing between serious cases of abuse of power involving sexual harassment, and those which do not deserve to be taken seriously. And she will need to avoid making unsustainable statements of intent, of the kind made on 8th October 1993 by John Major when he launched his “Back to Basics” campaign at the Conservative Party Conference.

Gyles Brandreth relates, in his diary for 18th October 1993, how this immediately became a stick with which the media beat the Prime Minister:

“As Mrs T launches her memoirs, she tells us the PM is now back on ‘the true path’ and rejoices. At Drinks in the Lower Whips’ Office, we turn our minds to lower things: Steve Norris [Conservative MP for Epping Forest] and his five mistresses. We are full of admiration. It is amazing – and amusing – apparently Mrs Norris knew what was going on, it was the mistresses who were unaware of one another – but utterly maddening for No. 10. ‘Back to basics’ was never supposed to be about sexual morality. Jonathan Hill [Major’s Political Secretary] tells me, ‘It hasn’t backfired. We’re sticking with it. This Norris nonsense will blow over. It’s a nine-day wonder. People wanted the PM to have a theme. Returning to our core values is his theme and he’s sticking with it. It’s working for us.'”

Hill was mistaken. A seemingly unending series of sexual and other scandals involving Conservative MPs caught in all sorts of absurd and despicable activities was exposed by the media. “Tory sleaze” obscured the good things done by the Major Government, and overwhelmed his reputation for respectability.

May became Prime Minister in part because of her unblemished reputation. So, in 1963, did the 14th Earl of Home. He was one of the high proportion of PMs in modern times – much higher than in the population as a whole – who have professed a serious religious faith, or have at least been steeped in Christianity while young.

Tony Blair was confirmed as an Anglican while at Oxford, Gordon Brown was a son of the manse, David Cameron said that when he thought of home (an old rectory) he thought of church, and May’s father was an Anglo-Catholic vicar.

None of this made them immune to scandal when it came. But it did perhaps help them to convey a reassuring sense of trustworthiness and hence of respectability.

Once respect goes, a Prime Minister is doomed. By 1922, David Lloyd George was very widely distrusted at Westminster. The sale of honours was that great Prime Minister’s most conspicuously shameless practice, but by no means the only one. The Conservatives ended their coalition with him, cast him into a wilderness from which he never returned, and replaced him for most of the next 15 years with the less brilliant but altogether more respectable figure of Stanley Baldwin.

Baldwin used his respectability to rout opponents as various as the press barons and Edward VIII. For a long time he and Neville Chamberlain also kept Winston Churchill out of things. But against Hitler, mere respectability proved useless.

May’s respectability helped her to become Prime Minister. But it will only enable her to remain so if she can adapt herself to very rapidly changing notions of what constitute respectable sexual behaviour and respectable employment practices; changes which have left many of her fellow MPs feeling deeply confused.