We have gone demented. Two Britons are or were (not very) ill from flu. "This could really explode," intones a reporter for BBC News. "London warned: it's here," cries the Evening Standard. Fear is said to be spreading "like a Mexican wave". It "could affect" three-quarters of a million Britons. It "could cost" three trillion dollars. The "danger", according to the radio, is that workers who are not ill will be "worried" (perhaps by the reporter) and fail to turn up at power stations and hospitals.

Appropriately panicked, on Monday ministers plunged into their Cobra bunker beneath Whitehall to prepare for the worst. Had Tony Blair been about they would have worn germ warfare suits. British government is barking mad.

What is swine flu? It is flu, a mutation of the H1N1 virus of the sort that often occurs. It is not a pandemic, despite the media prefix, not yet. The BBC calls it a "potentially terrible virus", but any viral infection is potentially terrible. Flu makes you feel ill. You should take medicine and rest. You will then get well again, unless you are very unlucky or have some complicating condition. It is best to avoid close contact with other people, as applies to a common cold.

In Mexico, 2,000 people have been diagnosed as suffering swine flu. Some 150 of them have died, though there is said to be no pathological indication of all these deaths being linked to the new flu strain. People die all the time after catching flu, especially if not medicated.

Nobody anywhere else in the world has died from this infection and only a handful have the new strain confirmed, most in America and almost all after returning from Mexico. A couple from Airdrie who caught the flu on holiday in Cancun are getting better. That tends to happen to people who get flu, however much it may disappoint editors.

We appear to have lost all ability to judge risk. The cause may lie in the national curriculum, the decline of "news" or the rise of blogs and concomitant, unmediated hysteria, but people seem helpless in navigating the gulf that separates public information from their daily round. They cannot set a statistic in context. They cannot relate bad news from Mexico to the risk that inevitably surrounds their lives. The risk of catching swine flu must be millions to one.

Health scares are like terrorist ones. Someone somewhere has an interest in it. We depend on others with specialist knowledge to advise and warn us and assume they offer advice on a dispassionate basis, using their expertise to assess danger and communicating it in measured English. Words such as possibly, potentially, could or might should be avoided. They are unspecific qualifiers and open to exaggeration.

The World Health Organisation, always eager to push itself into the spotlight, loves to talk of the world being "ready" for a flu pandemic, apparently on the grounds that none has occurred for some time. There is no obvious justification for this scaremongering. I suppose the world is "ready" for another atomic explosion or another 9/11.

Professional expertise is now overwhelmed by professional log-rolling. Risk aversion has trounced risk judgment. An obligation on public officials not to scare people or lead them to needless expense is overridden by the yearning for a higher budget or more profit. Health scares enable media-hungry doctors, public health officials and drugs companies to benefit by manipulating fright.

On Monday the EU health commissioner, Androulla Vassiliou, advised travellers not to go to north or central America "unless it's very urgent". The British Foreign Office warned against "all but essential" travel to Mexico because of the danger of catching flu. This was outrageous. It would make more sense to proffer such a warning against the American crime rate. Yet such health-and-safety hysteria wiped millions from travel company shares.

During the BSE scare of 1995-7, grown men with medical degrees predicted doom, terrifying ministers into mad politician disease. The scientists' hysteria, that BSE "has the potential to infect up to 10 million Britons", led to tens of thousands of cattle being fed into power stations and £5bn spent on farmers' compensation. A year later, the scientists tried to maintain that BSE "might" spread to sheep because, according to one government scientist, "the absence of evidence is not evidence of absence". The meat industry was wrecked and an absurd ongoing cost was imposed on stock farmers with the closure and concentration of abattoirs.

This science-based insanity was repeated during the Sars outbreak of 2003, asserted by Dr Patrick Dixon, formerly of the London Business School, to have "a 25% chance of killing tens of millions". The press duly headlined a plague "worse than Aids". Not one Briton died.

The same lunacy occurred in 2006 with avian flu, erupting after a scientist named John Oxford declared that "it will be the first pandemic of the 21st century". The WHO issued a statement that "one in four Britons could die".

Epidemiologists love the word "could" because it can always assure them of a headline. During the avian flu mania, Canada geese were treated like Goering's bombers. RSPB workers were issued with protective headgear.The media went berserk, with interviewers asking why the government did not close all schools "to prevent up to 50,000 deaths". The Today programme's John Humphrys became frantic when a dead goose flopped down on an isolated Scottish beach and a hapless local official refused to confirm the BBC's hysteria. The bird might pose no threat to Scotland, but how dare he deny London journalists a good panic?

Meanwhile a real pestilence, MRSA and C difficile, was taking hold in hospitals. It was suppressed by the medical profession because it appeared that they themselves might be to blame. These diseases have played a role in thousands of deaths in British hospitals - the former a reported 1,652 and the latter 8,324 in 2007 alone. Like deaths from alcoholism, we have come to regard hospital-induced infection as an accident of life, a hazard to which we have subconsciously adjusted.

MRSA and C difficile are not like swine flu, an opportunity for public figures to scare and posture and spend money. They are diseases for which the government is to blame. They claim no headlines and no Cobra priority. Their sufferers must crawl away and die in silence.

simon.jenkins@theguardian.com