Investigations are continuing to find the source of a foot-and-mouth outbreak in Surrey.

The virus was discovered on a farm near Guildford in Surrey and more than 100 cows have been slaughtered as a precaution.

According to reports, the investigation is centering on the nearby Institute for Animal Health in Pirbright in Surrey as the possible cause of the infection. The virus is stocked in the laboratory and it has emerged that the virus found on the farm was the same strain.

It has been reported that flooding may have played a part in the infection.

A nationwide ban on the movement of cows, sheep and pigs has been put in place, as well as an export ban. However, no new cases of foot-and-mouth have been reported in the last 24 hours.

Protection and surveillance zones have also been set up around the infected area.

Prime Minister Gordon Brown has visited the area affected by the outbreak and also met with local representatives of the National Farmers' Union and staff at a regional disease control centre in Reigate.

Mr Brown thanked local farmers for their "support and understanding" and pledged that "no resource will be spared" in dealing with the infection.

The Prime Minister said: "We have more than 150 people out in the field making sure it is possible to carry out tests and check the area. We also have hundreds of people around the country doing a magnificent job to make sure all the preparations to control the disease are carried out.

"This is a major national effort, the focus of which is to contain and control the disease and then eradicate it."

Mr Brown also said that around 100 farming establishments had been checked in the area surrounding the affected farm and that it was important to keep an "open mind" about the source of the infection.

He also said that the government was determined to gather "all the information necessary" before making a decision on the lifting of a livestock transport ban implemented on Saturday.

However, Conservative leader David Cameron expressed concern about reports that a farmer had seen walkers crossing the farmland within the exclusion zone around the farm. He said: "Of course we want the countryside to be open for business, but within the exclusion zone it's very important that people don't actually walk from farm to farm, otherwise there will be a risk of spreading it."

Mr Cameron also warned that the anger of farmers would be justified if it turned out that the virus was released from the Pirbright laboratory. He said: "The government will have some serious questions to answer about the report, which came out in 2002, that said the facilities were shabby and not up to standard.

"Farmers up and down the country are going to be quite angry because they have done masses to improve their own biosecurity and they are all suffering at the moment, apparently because of mistakes made at a laboratory which is meant to stop foot-and-mouth.

"Obviously the government have questions to answer because Pirbright is a government facility and the next-door factory is licensed and inspected by the government. But we shouldn't jump to conclusions."

(KMcA)