But the way that the story, gathered by a journal known in the trade as the "News of the Screws", meandered into a mid-market paper and then into broadsheets is significant. It tells us that there is no longer a fire-break where privacy issues are concerned. If the tabloids discover your sexy secrets one day, expect to see them retailed in more discerning prose in the quality broadsheets the next. In a market driven by the frenzy of competition, traditional divisions blur. Virtually all the news is now deemed fit to print by almost all of the papers.
Compare Mr Johnson's treatment with that meted out to the columnist Polly Toynbee. Two years ago, the Daily Mail printed details of her private life. The defence of the paper's editor, Paul Dacre, was that the public had a right to know Ms Toynbee's domestic circumstances because she wrote columns in favour of making divorce easier.
Note that Mr Johnson is being upbraided because he wrote about the sanctity of marriage while failing to meet his own exacting standards, while Ms Toynbee, in the eyes of the Mail, was guilty of not writing about her relationship with a married man, even though her liberal views on social policy meant that she could not be accused of contradiction between what she wrote and what she did. In both cases the justification given for publication was that traditionally applied only to holders of public office.
I should not appreciate a newspaper combing through my life. Few of us have records so unblemished that they could not, with a little flair, be turned into a story for a dull news day. But for too long, the press has enjoyed a one-way relationship with privacy. Like the ladies' tea circle in Congreve's Way of the World, we "came together like a coroners' inquest to sit upon the murdered reputations of the week". Now we awaken to the rude fact that the destroyed reputation is just as likely to be our own.
The only watertight solution appears to be to publicise your own scandal before others get to it. Rupert Murdoch - who knows a thing or two about handling the media - chose this option when he allowed his own New York Daily Post to report his separation from his wife.
The private space of public figures is contracting. At the same time, the definition of what constitutes a public figure is widening, and now seems to apply to anyone who is briefly in the limelight. So privacy is being eroded from both ends. It is easier than you might think to move from being a private figure to a public one - a careless omission in the "no publicity" box when you next fill in the lottery numbers and it could, as they say, be you.
Defining and upholding privacy is thus one of the most difficult tasks of an age addicted to information. A Demos paper, published next week, tries to make sense of this and adapt our attitudes accordingly. The author believes that the defence of public interest is insufficient to justify present levels of media intrusion. His solution is to impose on the media a "Special Duty of Scrutiny", which gives the press the right to override personal privacy " in certain circumstances but only if there is a reasonable basis for suspicion and no alternative way to collect the information".
The naive assumption here is that journalists start breaching privacy when they have no reasonable basis for suspicion and there are plenty of harmless ways open to them in their researches. It conjures up an image of men in macs deciding to camp out on a damp door-step in December just for the hell of it.
But the idea of the press being "granted" a right to collect and use private information "subject to specific authorisations" could come straight out of my copy of the East German Handbook for Socialist Journalists (1958 edition). Demos's worthy notion of splitting the difference between a privacy law and a state dispensation is a dangerous path to tread.
Neither can I imagine any such law that would substantially improve on the laws of tort on harassment, trespass and tapping without doing more harm than good. The best deterrent against press excesses in the past few years has been the increased level of libel awards. The simplest way to give ordinary people better redress against newspapers may well be to increase ease of access to m'learned friends through a no-win-no-fee provision. Judges and juries are not unaffected by the concerns of the public about privacy. So their decisions are increasingly likely to be sympathetic to plaintiffs.
Demos neatly classifies those of us with such minimalist views as "privacy fatalists". But I'm not sure that this is such a bad thing to be. Privacy fatalists acknowledge that there is a trade-off between what we wish to keep private ourselves and what we have a justified interest in knowing about other people.
Supporters of legislation argue that a law can be drafted that prevents intrusions into the private sphere yet allows investigative journalism to thrive. I doubt it. The line between them is too permeable.
Those countries that shield public figures from the kind of journalism that revealed Robin Cook's affair often allow their politicians to mislead on more serious matters. Francois Mitterrand led a licentious life, a fact well known in the Parisian elites but immune from discussion in the press. As a consequence, French taxpayers were kept in the dark - and still are - about the possible connections between Mitterrand's love life and his appointments to state broadcasting and at least one high political post.
In West Germany, the late Willy Brandt fell from office in 1974 when his aide Gunter Guillaume was revealed as a Communist spy. In the inquiry that followed, it emerged that the interior ministry had entertained suspicions about Guillaume for some time, yet it left the Chancellor at risk of treachery. This became one of the great unsolved mysteries of German political life.
We now know - from the East German security files, the Western ones on the period still being primly locked away - that Guillaume had been privy to Brandt's promiscuous sex life, and witnessed his use of young prostitutes. So a hostile intelligence service had compromising material on the Chancellor, and figures in one of his ministries knew that he was vulnerable. Yet for their own murky reasons they did nothing about it. Political journalists in Germany were well aware of the Chancellor's weaknesses. Strict privacy laws, and a press unhealthily deferential to the interests of politicians, prevented disclosure of a sex scandal which turned out to be the missing link in a story of immense political importance.
Harmful secrets will always fester if public figures are spared the harsher blasts of exposure. That is why it is worth upholding a press climate of bracing curiosity - even if it can be a tough and unforgiving one. The price of scrutiny, as Mr Johnson has just found out, is a heightened risk for anyone in the public eye of becoming infamous for 15 minutes.Reuse content