A question: what newspaper in the world proudly boasts every day that it prints all the news that's fit to print? The answer: the stately, majestic New York Times. And so what did it do when the London Times printed a prominent front-page story on Friday 13 February ("Dirty tricks row hits race for president") and the Daily Telegraph published no fewer than two similar stories ("Kerry faces big test in internet storm about mystery woman" and "Campaigners in crisis mode amid fears of 'bimbo eruption'")? Or when the Sun ("New JFK hit by scandal") actually printed the name of the young woman alleged to have had an affair with John Kerry, quoting her parents as saying Kerry was a "sleazeball"?

The answer is that the New York Times did precisely nothing. As did the Washington Post. As did the vast majority of mainstream newspapers and television channels in the US; their readers and viewers remained in the dark about the accusations being made against Kerry. Why? Media outlets in the US have more integrity than those in Britain, and because the allegations were unsubstantiated they refused to touch such a sensational and (as we were to discover) probably groundless story. But the gleeful allegation with no proof whatsoever was published in the right-wing Drudge Report on the internet, and that was all the British newspapers needed for a source; the result was that British newspaper readers were reading of the allegations long before their American counterparts.

For serious American editors, the internet age has presented them with serious problems. Drudge's story was published the day before the British papers went to town on the story. Matt Drudge claims that he had 15 million visits to his website that day. The story had previously surfaced on obscure websites, too, but the moment Drudge published his story it became the talk of political Washington.

Yet not until last Tuesday, after Alexandra Polier, 27, denied the claims ("I have never had a relationship with Senator Kerry, and the rumours in the press are completely false") - and there came an about-turn from her parents as well as an insistence that they had been misquoted by the Sun ("we appreciate the way Senator Kerry has handled the situation and intend on voting for him as president of the United States") - did the New York Times and the Washington Post see fit to present reports of the denials.

Drudge publishes gossip, some of which is true and some not; his main claim is that he first published the Monica Lewinsky story, which turned out to be deadly accurate. His sources are often mainstream journalists whose editors will not print or broadcast their stories because of insufficient sourcing; other gossip is given to him as "spoilers", when journalists know that a rival is planning a scoop on some particular story and they pass on enough information on the subject to Drudge to steal the other's thunder. And some is passed on as part of a dirty-tricks campaign by rivals, which may be the case in this story: were the Republicans to blame?

To complicate matters still further, Kerry is known as a womaniser (one woman told me disgustedly that he had given her the "hairy eyeball", which is a new expression to me) and when he finally married Teresa Heinz in 1995 - after 12 years of de facto bachelordom - his staff breathed a sigh of relief that the frequent bimbo stories he attracted would end. That made it all the more difficult for the editors this time round, because such a story about Kerry was plausible.

The Drudge story was quickly seized upon and used by right-wing talk radio - a potent political force in America these days - and by odd newspaper websites such as those of the Chicago Sun-Times and the Philadelphia Daily News. Some television stations went with the story, too. But it was not until the denials came that the story became fair game for most of the mainstream media.

So what's an honest editor to do? Timothy Noah, in the online magazine Slate, produced an entertaining list of pretexts by which the subject of Kerry's alleged adultery could be aired with apparent legitimacy in the mainstream media. It could be discussed as an issue of ethics for news organisations - to publish or not to publish. It could be presented as a sociological analysis of the internet phenomenon. It could be used as an illustration of how vicious the presidential election has already become. It could be published as a tongue-clicking case of sexual harassment of a young woman (who has actually said she was never an intern for Kerry). It could be used in a discussion about Kerry's character, or about hypocrisy by political candidates. I would add another method, too, used frequently in the Clintonesque scandals - re-report what "prestigious" London papers, which picked up the story from Drudge or elsewhere, are saying. And so the merry-go-round whirls on.

Kerry himself merely stoked the fires when he issued his first denial of the allegations on a radio talk show hosted by a popular DJ, Don Imus. "There is nothing to report, nothing to say, the answer is no," he said, somewhat unconvincingly. Only last Monday did an unequivocal, categorical denial come "for the last time" from him - on the same day that Drudge changed the man who was supposed to have had an affair with Polier from Kerry to his finance director, Peter Maroney.

I suspect, none the less, that the issue of womanising may come to dog Kerry again in this campaign. His wife, the 65-year-old Teresa Heinz Kerry - worth a reputed $500m - is not an electoral asset. The American electorate expects an adoring wife to gaze lovingly at her spouse as he delivers boring speech after speech - Nancy Reagan was the champion in this respect - but Teresa Heinz Kerry often merely scowls at her second husband (her first husband, John Heinz, of the Pittsburgh baked beans fortune, was killed in a plane crash in 1991). She hugely embarrassed Kerry by saying she had made him sign a prenuptial agreement.

So far, in these dirty-tricks wars, it has emerged reasonably authoritatively that Boy George put in only 82 full days of National Guard service during the Vietnam war. And now that Kerry is close to becoming the crowned Democratic candidate to take on Boy George following his primary victory in Wisconsin last Tuesday - although the relentlessly bright and smiley Senator John Edwards, who came a close second, could yet surge dramatically and give him a shock on Super Tuesday, 2 March - the Republicans are busily scouring everything they can find that Kerry has either said or done.

They might be interested in an article in the 18 February 1970 issue of the Harvard Crimson, the university students' newspaper. Kerry is now unashamedly making much of his heroism in Vietnam, but what caught my eye was a casual, throwaway line in an article that described Kerry's first run for Congress in Massachusetts. "When he approached his draft board for permission to study for a year in Paris," the Crimson said, "the draft board refused and Kerry decided to enlist in the navy." In other words, Kerry tried to avoid service in Vietnam in the first place. Now how about that, the Sun, the Daily Telegraph and the Times?