During his briefing to journalists that day, the Foreign Secretary announced that a rape camp had been set up in Kosovo. Robin Cook accused the Serbs of separating refugee women from their families and herding them into a camp in the village of Djakovica, near the Albanian border, a claim which recalled the Serbs' use of rape as a tactic in Bosnia in the early 1990s. Yet Mr Cook's claim added little to a detailed briefing on the same subject by the Pentagon several days earlier. He also used a strikingly equivocal formulation - "The story has come from a number of women and, sadly, it does seem to have the ring of corroboration" - instead of producing hard evidence.
Something similar happened the following day when Mr Robertson briefed journalists that the indicted war criminal Ratko Mladic was now leading a commando unit in Kosovo. Once again no hard evidence was produced, recalling Mr Robertson's claim earlier in the war that the Serb paramilitary leader Zeljko Raznatovic, known as Arkan, had joined operations in Kosovo. Shortly afterwards Arkan was spotted in Belgrade, apparently paying more attention to his social life than his military engagements. Not long after Mr Robertson made this allegation, news began to emerge of the deaths of many civilians in a terrible incident, or series of incidents, which appeared to include the bombing in error of a refugee convoy by a Nato warplane. Newspapers were soon publishing horrifying pictures of dead and injured civilians.
It was at this low point in Nato's fortunes that the President of the United States chose to reveal that Yugoslavia has stockpiled chemical weapons. Bill Clinton promised a "swift and overwhelming" response to the use of such weapons by the Serbs, while the Pentagon said Nato planners had avoided attacks on three known stores of chemical agents to avoid releasing deadly fumes into the atmosphere. Mr Clinton is our closest ally but that does not alter the fact that, on at least two occasions, he has launched air strikes on foreign countries to divert attention from domestic difficulties. Last August he ordered missile attacks on what was claimed to be a chemical weapons plant on the outskirts of Khartoum - risking the release of poisonous fumes over that city. Fortunately the claim turned out not to be true, and only one person died in an attack on a plant, the function of which was the manufacture of more than half the human and veterinary medicines used in Sudan.
I have no way of knowing whether the Yugoslav president, Slobodan Milosevic, has chemical weapons. But I do know that Mr Clinton is a congenital liar. In Britain his closest equivalent for mendacity is the Sun newspaper which last week added another outrage to its stockpile of lies. While more cautious reporters tried to discover if a Nato bomber had unintentionally been responsible for the deaths of around 70 Kosovar civilians, the Sun blamed the tragedy on the Serbs. "Serb troops slaughtered hostage refugees yesterday - then blamed Nato planes for the massacre", it blustered.
It is a dismaying realisation that we do not expect better of the Sun. But I would like to think British ministers are operating to higher ethical standards, not reporting rumour as fact and displaying a reluctance to accept collective blame when something goes wrong. Mr Cook and Mr Robertson have particular reason to weigh their words carefully, given that both are veterans of the "Iraqi boy" fiasco - the story of a child supposedly imprisoned for throwing stones at a picture of Saddam Hussein, which has never been verified despite persistent questioning in the House of Commons.
What the British government is attempting in Yugoslavia, even if it is going about it rather ineptly, is the pursuit of a new foreign policy whose aims are humanitarian and altruistic instead of being based on narrow considerations of self-interest. It would be tragic if this brave and risky enterprise were to founder because of an unthinking reliance on old-fashioned smear tactics of the type favoured by the Sun and Mr Clinton.