WE HAVE most of us done it at one time or another. The cause may be drink, lust, a desire to show off or, more usually, simple foolishness. We may act on impulse, going for a silly walk with troublesome consequences. Usually they last only a few days. What the newspapers call a gaffe - one of those words, like "zany", used exclusively by the press rather than in ordinary discourse - can commonly be repaired by an apology, a note, a present, most of all the passage of time. The embarrassment can still bring a blush to the cheek at the mere thought. But it can equally well become the foundation for a humorous anecdote, polished over the years by endless retelling, at first amusing, finally tedious.

Sometimes, however, matters do not work out so conveniently. The episode changes lives and ruins a career. Things are never the same again. One such victim is before us today. It is always sad to see a reputation in shreds. I refer, of course, to Mr Alastair Campbell.

As confessions seem to be in fashion, I shall now make one of my own. On the morning following Mr Ron Davies's resignation, I was putting in an appearance on Talk Radio to publicise the paperback edition of my book The Road to Number 10 (Duckworth pounds 12.95). My fellow-guest was the engaging and ubiquitous Mr Matthew Parris, a figure as omnipresent in the political life of the nation as ... well, as Mr Peter Mandelson.

In all the talk, by the way, around the BBC's prohibition of any discussion of Mr Mandelson's private life, which was caused by Mr Parris's observation on Newsnight, no one has said anything about the originator of the ban, the corporation's political adviser, Ms Anne Sloman (formerly Duncan-Jones). Originally it was thought that Ms Sloman had acted entirely on her own initiative. Now it is being claimed that her instruction flowed from a telephone call from Mr Mandelson to Sir Christopher Bland, the BBC chairman. I used to know her in the early 1970s, when I was an occasional presenter of The Week in Westminster, and she the regular producer. She was a tremendous bossyboots even then.

Once I was conducting an interview with the late Eric Heffer. After it was over she bustled into the studio, announced her disappointment at our endeavours and instructed us to go through it again. I said I thought the interview had been perfectly all right. Heffer agreed, in more vigorous language. He had, he said, no intention of redoing the interview, having better things to do with his valuable time.

Ms Sloman persisted in her view. I weakened not only because I am, like most Welshmen, anxious to please, but also because I knew that as producer Ms Sloman was the boss. Heffer was made of stronger stuff. It was a case of the irresistible force and the immovable object. Eventually the object moved. With much muttering, he agreed to do the interview again. Afterwards Ms Sloman bounced in. "That was much better," she said. In fact - by which I mean, as people usually do when they use the expression, in my opinion - it was no better, no worse, but much the same.

Anyway, in that other studio some years later on, Mr Parris maintained that, so far from behaving with resolution and skill, Mr Campbell had behaved foolishly. He and Mr Tony Blair had added to the mystery instead of solving it. The majority view of the press at this point was that Mr Campbell and Mr Blair had behaved decisively, even if ruthlessly.

How different, how very different, from our home life under dear Mr John Major! In those unhappy times an erring minister's hand would be detected in till or up skirt; whereupon Mr Major would declare his unshakeable loyalty to the politician concerned. If a till was involved, he would say that no offence had been committed and demand further evidence. If it was a skirt, he would say (as Mr Davies has been doing, though skirts not much in view) that people's private lives were their own business.

Then our brave lads would go into action with their lethal chequebooks, dreaded tape recorders and sworn affidavits; the scandal would turn out to be much juicier than anyone had supposed; and the wretched minister would depart in shame after being ceremonially stripped of his official car. The one-sided battle generally took about three weeks before Fleet Street's Finest could claim yet another regimental honour.

Mr Campbell and Mr Blair were determined to avoid the opportunity for any such victories over the new administration. I agreed with most of my colleagues rather than with Mr Parris that, over Mr Davies, they had succeeded. But (and here the element of confession enters into it) I was wrong. Not only had Mr Davies himself failed to be open about what happened on Clapham Common and in adjacent regions of south London on the night in question. Mr Campbell had not been entirely frank either. Nor had our truth-telling Prime Minister, who went on television during the Bernie Ecclestone affair to say: "Trust me, I'm a politician."

The line pursued by Mr Campbell and Mr Blair was that, though they might not be entirely clear about the events on and around the Common that evening, their ignorance was due to the unforthcoming policy being pursued by Mr Davies. Mr Campbell went further:

"There is no evidence at all of any gay link or drug link. There are no salient facts in our possession that are not in yours."

Those were his fatal words. But it now appears that Downing Street, early on that Tuesday morning, were in possession of facts which no one else knew except Mr Davies and the police. It was the deputy commissioner of the Metropolitan Police who informed first Mr Jack Straw and then No 10. It was Mr Blair who summoned Mr Davies, not Mr Davies who asked whether he could call on Mr Blair. The Treasury Solicitor vainly threatened the Sun with legal action if it made "any suggestion of homosexual activity". Even before Mr Davies resigned, Mr Alun Michael had been instructed to prepare himself for his new responsibilities as Welsh Secretary. Though he is trying to play with the word "salient", Mr Campbell has manifestly been telling what Mr Chris Patten used to call "porkies" when he was seeking the demotic touch. Having made a thorough mess of Mr Davies's resignation, Mr Campbell and Mr Blair are now set to make an even more comprehensive dog's breakfast of the consequences of that resignation. Last week I advised Mr Michael not to allow himself to be forced into contesting the leadership of the Welsh Assembly, a post to which Mr Davies was to have moved next year, having defeated Mr Rhodri Morgan for the nomination. I told him, but he wouldn't listen. The foolish fellow is prepared to fight Mr Morgan for the job.

If he wins, he will have to leave the Cabinet after only a few months and will never be heard of again, getting wetter and wetter in the soft rain coming off the Bristol Channel. But he may not win. Mr Morgan may be the victor. He certainly deserves to be. Why my colleagues call him a "maverick" I do not know. All he has done, apart from smoke out a few Welsh quangocrats appointed by the Tories, is summon Mr Campbell before the Commons committee over which he presides. Clearly, the time has come for him to order Mr Campbell to turn up a second time.