That virus can be fatal if it is passed on to humans and further tests will determine if it is the same strain as found in Asia. Britain's Department of Environment, Food and Rural Affairs (Defra) and the European Commission is carrying out the tests, and Defra has said that the 159,000 other turkeys on the farm will also have to be slaughtered.

According to an EC statement, a threekilometre protection zone and a 10km surveillance zone will now be set up at the farm in Holton, Suffolk.

The statement added: "Strict movement controls are in place, poultry must be kept indoors, there is a prohibition on gatherings of poultry and other birds and on-farm biosecurity measures will be strengthened."

A Defra spokeswoman said the risk of the disease spreading to humans was low and there was no need for panic.

Professor John Oxford, a virologist at the London Queen Mary's School of Medicine and Dentistry, said he was confident the outbreak could be contained. "I don't think it has made any difference as a threat to the human population. The most likely explanation is that a small bird has come in through a ventilation shaft.

"One good thing about this virus is that it's easily destroyed. You can kill it with a bit of detergent. You want to move in and take action straight away and I'm sure they'll be doing that, " Oxford said.

Defra said the alarm was raised by the farmer after he noticed "significant mortality" among his flock. The first deaths happened on Tuesday, when 71 chicks died. A further 186 died the following day, 860 on Wednedsay and some 1,500 died on Thursday, making a total of 2,617.

In May last year, more than 50,000 chickens were culled after an outbreak of the H7 bird flu in farms in the neighbouring county of Norfolk. One member of staff at the farm contracted the disease and was treated for an eye infection.

In March 2006, a wild swan found dead in Cellardyke, Fife, was found to have the H5N1 strain of the virus, which has been responsible for the deaths of more than 100 people, mostly in Asia.

FLU FACTS

»There are 15 types of bird (avian) flu.

»The most contagious strains, which are usually fatal in birds, are H5 and H7.

»There are nine different types of the H5 strain.

»The nine types take different forms - some are pathogenic, others are harmless.