The foot-and mouth outbreak is unlikely to have spread outside Surrey, the government has announced.
Meanwhile, the BBC has learned that initial tests at a farm outside the existing 10km (6.2 mile) surveillance zone are negative.
Two farms near Guildford have tested positive for the disease, while animals culled at a third inside the zone did not have foot-and-mouth, Defra said.
Gordon Brown has said the UK is "open for business" following the outbreak.
The Department for Environment, Food and Rural Affairs (Defra) said Hunts Hill Farm inside the surveillance zone, where 362 cows, sheep, pigs and goats were destroyed as a precautionary measure, did not have the disease.
Farmer John Emerson voiced his frustration after it was confirmed the slaughtered animals were not infected.
He said: "When we first heard the herds next door to ours were infected we thought it was inevitable ours would get it too.
"But knowing now that my animals were never infected makes it worse."
There was "clinical suspicion" of foot-and-mouth at a farm at Wotton, near Dorking.
The farm is outside the surveillance zone but a 3km (1.8 mile) temporary protection zone has been put in place.
Government sources have told the BBC a second batch of results from the Wotton farm are likely to be available later on Friday.
Earlier, Laurence Matthews, who leases the farm, said he was "absolutely sure" his cattle did not have foot-and-mouth, but he called a vet as a precaution.
Chief veterinary officer Debby Reynolds briefed reporters on an interim report into the outbreak.
She said: "It sets out that the most likely scenario is that the infection will be restricted to the Surrey area. But it does set out alternatives."
HOW FOOT-AND-MOUTH SPREADS
Direct contact, from animal to animal
Fluid from an infected animal's blister; saliva, milk or dung also pass on the disease
Animals eating infected feed
Virus can be spread by people or vehicles, if not disinfected
Airborne spread of disease also possible
Animals can begin spreading virus before visible signs of disease emerge
The report also found the most likely source of the outbreak was the nearby Pirbright lab site, used by vaccine manufacturer Merial and the state-run Institute for Animal Health.
Ms Reynolds added: "It concludes that the risk of spread of infection out of Surrey through undisclosed infection in sheep during the risk period is very low.
"And this report - and it's an interim, initial report - sets out the most likely scenario that whilst there is a risk of further outbreaks in the same area, it is unlikely that infection from the original release of virus will occur.
"However, further cases could occur through secondary spread."
She also said a programme of vaccination would not be carried out but the situation would be reviewed daily.
Prime Minister Mr Brown said everything was being done to get the UK back to normal outside the restricted zones.
Restrictions on taking animals to abattoirs have been lifted but many movements of livestock - such as sending animals to market - are still banned.
He said farmers would be compensated for clean-up costs on top of normal compensation, and payments would start going out "in the next few days".
"We have restricted the disease to a limited area of this country. The risk of it spreading out of these areas is low if not negligible," he said.
Mike Giffin, chairman of the Surrey branch of the National Farmers' Union, said foot-and-mouth was "under control" at the moment.
The first cases of foot-and-mouth were found in cattle at Woolford Farm, near Guildford, last Friday and a second outbreak was confirmed at a neighbouring farm on Monday. Cattle in both cases have been culled.