Experts were tonight probing whether the recent floods in England may be behind the foot and mouth outbreak, as the battle to contain the disease continued.
The Government’s chief vet Debby Reynolds said high water levels could have helped spread the virus on the Surrey farm at the centre of the crisis.
Tests are still being carried out to confirm whether the nearby Pirbright research site – where the disease was being kept in order to produce vaccine - was the source of the outbreak.
The news came as Gordon Brown announced he was abandoning his holiday in order to oversee the emergency response.
Mr Brown is expected to be joined by his family at the Prime Minister’s country retreat, Chequers, rather than returning to Dorset.
This morning he sought to reassure farmers that officials were working “night and day” to stamp out the problem.
Speaking on a visit to the Regional Disease Control Centre in Reigate, Surrey - which is co-ordinating efforts to deal with the disease at a local level – Mr Brown said a major national effort was under way to “contain, control and eradicate” the disease
“I understand that this is a difficult time for (farmers) and appreciate their anxiety and worry,” he insisted.
“This is a major national effort, the focus of which is to contain and control the disease and then eradicate it.”
Farmers’ representatives said the industry would be “horrified” if it emerged that the disease originated at the research laboratory in Pirbright, Surrey, at the centre of the investigation.
The site is shared between the Institute for Animal Health (IAH), a diagnostic and research centre, and pharmaceutical company Merial Animal Health, whose work includes manufacturing vaccines.
Both organisations use the strain of the virus detected in the slaughtered cattle, but both have insisted there was no evidence of breaches in biosecurity at their labs.
Government officials were continuing to investigate any link between the site at Pirbright and the outbreak around three miles away. A report into the outbreak, ordered by Mr Brown at the weekend, is expected tomorrow.
Dr Reynolds told a press conference in central London today that there was interest in a flooded area on the farm, which is close to the village of Normandy, outside Guildford.
Some 97 cows were slaughtered on neighbouring premises after the virus was identified, although no new cases have been identified over the past 24 hours.
Dr Reynolds said: “The investigation on the farm is taking all factors into account including flooding, movement, and everything that is related to events in the lead-up period to the report of suspicion being made.
“There is interest in a particular area on the farm where there was some flood water and that is one of the features that is being examined.”
She also said production of a vaccine for potential use in controlling the spread of the disease will be carried out by the Merial Animal Health Laboratory. Merial tonight announced it was temporarily recommencing production of the vaccine, but added that the suspension of all other production would continue.
Farmer Derrick Pride, whose cattle were slaughtered after they were found to be infected on Friday, said yesterday: “It is nothing to do with us. It is not our fault. It is something beyond our control.”
A nationwide ban on the movement of cows, sheep and pigs and the export of cloven-hoofed animals and animal products was enforced within hours of the disease being diagnosed.
Protection and surveillance zones were set up around the infected farm, where cattle were slaughtered on three sites, and later extended to include Pirbright.
Susceptible animals on an adjacent farm were also culled because of “potentially dangerous contact”.
But the Government faced Tory accusations of taking a “casual” attitude to the outbreak today, after refusing to shut footpaths near the outbreak.
Party leader David Cameron raised fears that walkers could spread the disease after being told by a farmer friend that people were freely crossing his land.
But Defra insisted they posed a negligible risk and that access would only be blocked within the 3km exclusion zone if scientists demanded it.
Peter Kendall, president of the National Union of Farmers, said its members were “angry and concerned” that the outbreak may be linked to the research centre.
Speaking at Downing Street, following a meeting with Mr Brown and Mr Benn, he said: “We all need good science, we need to have vaccines being produced.
“But it cannot be the case that we have a scientific institution that actually releases diseases into the environment.
“My members will be quite rightly horrified.
“We need to find a way of making sure it never ever happens again.”
Mr Cameron tonight resumed his holiday in France, leaving shadow foreign secretary William Hague at the helm of his party.
A spokesman for the Tory leader said shadow home secretary David Davis would take over from Mr Hague later this week, while shadow chancellor George Osborne is due to assume day-to-day control next week.
“Mr Cameron will be kept in close touch with the situation at all times while he is on holiday,” the spokesman added.