“At this stage disease has not been confirmed, laboratory results will follow.

“In the meantime, and as always in such circumstances, I reiterate my message to animal keepers to practise the highest standards of biosecurity, remain vigilant for disease, and report any suspicions quickly.”

A spokesman for the National Farmers’ Union said: “We are having meetings and video conferences with Defra. We are trying to build up a picture of what is happening at the moment.”

John Gunner's cattle were culled last month

The spokesman said he did not have any information on the exact location of the farm or the identity of the farmer involved in the outbreak.

Experts had declared foot and mouth disease was eradicated and the last remaining restrictions on livestock were lifted on Saturday.

Angry farmers affected by the outbreak had called for the nearby Pirbright laboratory site, which has been blamed for the leak, to remain closed until the source is found.

A warning sign near Guildford

But chief veterinary officer Debby Reynolds said last week: “I’m satisfied that foot and mouth has been eradicated from the UK in 2007.”

Official reports blamed faulty drainage systems at Pirbright for leaking the disease, coupled with heavy rain, building work and construction vehicles moving from the site.

The Health and Safety Executive (HSE), which published its official report into the outbreak, said it was “pretty clear” that the virus escaped from Pirbright but said it was not possible to pinpoint whether the exact source was the Institute for Animal Health or Merial, which share the site.