"The decision was taken following clinical examination of animals on land in the existing protection zone as part of intensive surveillance in the area," Defra said in a statement.

"Samples are being taken for laboratory testing."

Cases have been confirmed on seven premises during the current outbreak which was first reported on a farm in Surrey on Aug 3.

The seventh positive test, also on a farm in Surrey, was confirmed on Monday.

There have been several suspected cases outside Surrey but no positive tests.

Prime Minister Gordon Brown has asked Environment Secretary Hilary Benn to examine whether farmers should be compensated for the outbreak of foot and mouth as well as the bluetongue livestock virus.

There have been 11 confirmed cases of bluetongue since the first case was reported last weekend in Suffolk.

The economic damage caused by these two outbreaks, resulting from lost production and restrictions on the movement of livestock, has been estimated at tens of millions of pounds.