The new case was discovered close to a farm south of London where an outbreak was first reported last month.
The Department for Environment, Food and Rural Affairs (Defra) was quick to impose a new England-wide ban on the movement of cattle, sheep, pigs and other ruminants.
The European Union also reimposed a ban on British meat exports to the bloc's 26 member states, the European Commission says.
Britain's red meat export market is worth about STG500 million ($A1.2 billion) a year, mostly with the EU.
Britain was the ninth largest beef exporter last year among the 27-member European Union.
Cattle were ordered slaughtered on the affected farm, near Egham, west of London.
Egham is 21km from the village of Normandy, where foot and mouth disease was confirmed on August 3.
A 3km protection zone was thrown around the farm holdings, with a wider 10km surveillance zone imposed on the farm.
Animals on the farm next to that site were to be slaughtered because they were suspected of having been infected, Defra says in a statement.
"This is a precautionary measure and was identified by Animal Health during surveillance this afternoon," it says.
After chairing a meeting of COBRA, Britain's top-level cell to cope with national crises, Prime Minister Gordon Brown vowed that his government would do everything to stamp out the disease and find its "root cause".
An official investigation last week concluded that the earlier outbreak was probably caused by leaking drains, flooding and vehicles moving from nearby animal vaccine laboratories without pinpointing the exact source.
The laboratories are at Pirbright, 16km from Egham.
A leading scientist, Professor Hugh Pennington, says the latest outbreak is highly likely to be a resurgence of the strain which hit farmers last month.
Mr Pennington, an emeritus professor of bacteriology at Aberdeen University, northern Scotland, says the disease could survive for as long as two months in cool, damp conditions, which the area has been enjoying in recent weeks.
Britain's Chief Vet Debby Reynolds says the authorities were vigilant after she confirmed the new case of foot-and-mouth disease.
"There are other reported cases being investigated, including one in Norfolk in some pigs, where foot and mouth disease can't be ruled out," Ms Reynolds says.
She added in a statement: "This is a developing situation.
“Our objective is to contain and eradicate the disease."