The fact that a biological research laboratory was probably the source of the foot and mouth outbreak is, paradoxically, both hugely reassuring and at first sight very worrying.

Comment: Reassuring???

Reassuring because if the multinational firm Merial Animal Health Labs was responsible for the outbreak, then scientists will know exactly which strain of the virus is responsible and will have a vaccine readily available - indeed, the cause of the outbreak would have been the very foot and mouth vaccines that the scientists are producing in huge quantities.

Comment: Insane wishful thinking!!!!

What's more, it will be known exactly where the outbreak began, and when.

Thanks to the prompt action by Surrey organic beef farmer Roger Pride (who should receive a medal for his vigilance), the source of the outbreak has been pinpointed immediately, reducing massively the chance of a nationwide epidemic.

We might yet avoid a repeat of the terrible scenes of six years ago.

But the news is also worrying because it highlights the fact that huge quantities of viruses and bacteria are held in laboratories all over Britain which we have been led to believe are safe. They include germs which have the potential to cause economic devastation and much worse.

According to Professor John Oxford, one of Britain's leading virus experts, outbreaks from labs are extremely unlikely.

His own biosecure laboratory at Queen Mary College in London contains samples of the SARS virus (which killed several hundred people in Asia five years ago) and also the H5N1 bird flu virus which some scientists say has the potential to mutate into a virulent, infectious strain which could kill millions of humans worldwide.

What would be the chances of, say, an animal rights extremist or Islamist terrorist getting a job as a lab assistant or even researcher in the laboratory, smuggling out avian flu or something equally nasty, and causing havoc?

"The rules are extremely strict," Professor Oxford says. "I would never allow a student into my lab. I have only three members of staff who are experienced enough to go in there, and they are all personally known to me."

Must assume, and hope,that similar rules are in place at other research establishments where such micro-organisms are kept.

Comment: Assume and hope?????

There are several - the largest including the Health Protection Agency labs in Colindale and the National Institute of Medical Research in Mill Hill, both North London, the Defra veterinary labs at Weybridge, Surrey, the Institute for Animal Health at Compton in Berkshire and, of course, the MoD's Porton Down in Wiltshire.

Foot and mouth has potential to wreak economic havoc, but at least it is harmless to humans. What about those other diseases - bird flu, Sars and worse, being kept in labs? Can we be sure they are all secure?

Mostly, but not entirely, is the answer. For nearly a century, there have been leaks - unwitting and deliberate - from a host of labs all around the world. Some deadly.

Back in 1952, in a British germ warfare test, a cloud of pneumonic and bubonic plague germs was deliberately released over a pontoon moored off the Outer Hebrides, on which there were cages of live monkeys and rabbits. Unfortunately, a fishing trawler sailed through the cloud and, quite incredibly, its crew were allowed to pilot the boat right back to the Lancashire coast without being stopped or warned, such was the culture of Cold War secrecy at the time. Fortunately, the trawlermen were not infected.

Numerous claims have been made over the years of "escapes" by various deadly pathogens from the Ministry of Defence's germ warfare establishment at Porton Down, where experiments on some of the most deadly pathogens and chemical weapons known to science have taken place since World War I.

Over the decades, tens of thousands of animals, including primates, have been deliberately infected with a host of ghastly diseases and have, inevitably, come into contact with hundreds of researchers, lab assistants and technicians.

According to Professor Hugh Pennington, an authority on infectious diseases, conditions are far better today than they were. Indeed, 30 years ago, "biosecurity", such as it was, was a shambles. "It was almost a tradition that every few years a microbiologist would die from the diseases they were working on. It has certainly improved a lot in the past few years."

In the early 1970s, a small outbreak of smallpox followed an accidental infection of a lab worker at the London School of Hygiene and Tropical Medicine. And the last human case of this horrible disease occurred after a technician was infected at Birmingham University in 1978. Today, smallpox exists in only two places, at the Centres for Disease Control (CDC) labs in Atlanta, Georgia, and Novosibirsk, Russia.

Diseases such as smallpox and Sars are now subject to Category 4 rules, which mean that they must be handled and stored in conditions of almost unbelievable security: sealed chambers with airlocks, staff dressed in full pressurised suits and a endless lists of safety rules.

Security is a particularly an issue in the U.S. Two years ago, three mice escaped from a laboratory in Newark, New Jersey. An FBI "mouse hunt" was declared after Richard Ebright, a microbiologist at Rutgers University, pointed out that the mice were carrying the Black Death - the disease that once killed a quarter of Europe's population. Yet the mice were never found.

And just last month, a federal agency ordered a biodefence laboratory at Texas A&M university to stop work on the Category B bioterror agent Brucella, a bacterium, after lab workers became infected and the disease prevention agency was not notified, as is required under federal law.

It is tempting to say that we should simply close these labs and that the risk they pose is too great. But, of course, such a proposal would leave us in far, far more danger. "You have got to grapple with infectious diseases," says John Oxford. "You can't grapple with them on the Moon, you have to do it on Earth."