Authorities sealed off a farm in Kent, southern England, and Chessington World of Adventures & Zoo, a theme park in nearby Surrey, on Tuesday because of suspicions of foot and mouth.
But Britain's Chief Veterinary Officer Debby Reynolds said preliminary tests had found no foot and mouth at either site.
The latest report on the outbreak concludes the risk of the disease spreading outside the infected area in Surrey is now very low, Reynolds told a news conference.
Tests from both places are negative, an agriculture ministry spokesman said.
The highly infectious virus was found this month on two farms in Surrey, forcing more than 570 animals to be destroyed and prompting the European Union and other countries to ban British meat and dairy exports. Farmers say the trade bans cost them 1.8 million pounds ($3.58 million) a day.
Chessington World of Adventures said it had called in a vet to examine one of its sheep following a daily health check. The zoo has been closed since early August as a precaution.
A national ban on animal movements has been in place since the outbreak was confirmed on August 3, although it was later eased to permit the movement of animals to slaughter, to milking or for emergency treatment.
EASING OF ANIMAL RESTRICTIONS
Restrictions on livestock movement will be further eased from midnight on Wednesday to permit farmers to move their animals between different fields on their farm for welfare reasons, the government said.
Provided ... there is no change in the disease situation, the chief veterinary officer will stand down vaccination teams from their current level of alert, an agriculture ministry statement said.
The government had teams ready to vaccinate animals at farms around the infected area if the outbreak had got out of hand.
Kevin Pearce, director of food and farming at the National Farmers' Union, said farmers would be relieved by the negative test results.
We have got to a stage where it is comfortable to start to look at the exit strategy, which is very important for us because it allows people to think that there is a light at the end of the tunnel, he told Reuters.
Farmers have generally praised the government for responding quickly to the latest outbreak, in contrast with a devastating 2001 outbreak when more than 6 million farm animals were killed, costing the economy some 8.5 billion pounds.
The government has said the likely source of the infection was the Pirbright research centre, close to the farm where cattle were first infected.
The site houses two foot and mouth laboratories -- one public and one, Merial, owned by U.S. firm Merck and French firm Sanofi-Aventis SA.
It remains unclear how the virus could have escaped from the laboratories, which say they have strict hygiene measures.
Foot and mouth spreads easily on the wind and causes animals to foam at the mouth and collapse.
(Additional reporting by Adrian Croft and Jeremy Lovell)