A spokesman said the disease was detected at a farm within the existing 3km (1.7-mile) radius protection zone in Egham, Surrey.
Animals at the infected farm have been culled as a precaution. The authorities are currently checking the area in Hampshire, on the south coast of England.
The discovery comes after the disease was confirmed in slaughtered cattle at four other farms in the same area earlier this month.
The first outbreak occurred not far from Guildford, Surrey, on August 3. The second outbreak was detected on a farm in the same area August 7.
Since August 3, about 1,800 animals in the infected area have been culled as a precautionary measure.
Confirmation of the disease caused the European Union to prolong its ban on British exports of meat, livestock and dairy products until October 15.
Meanwhile, the authorities confirmed Monday a second case of a bluetongue disease in Suffolk, east England.
Bluetongue is a very different infection to Foot and Mouth Disease and does not affect humans. The disease is transmitted by midges.
