A herd of cattle culled in Surrey on suspicion of foot-and-mouth has tested positive for the disease.
The farming industry is struggling to cope with movement restrictions
The herd was killed at a farm in Englefield Green near Egham as a precaution on Monday, Defra said.
The virus has now been detected at seven sites within an exclusion zone set up in the county last month.
Another suspected foot-and-mouth case is being probed in Hants. Meanwhile, a second case of the bluetongue virus has been found at a Suffolk farm.
The latest suspected foot-and-mouth case is in the West Tytherley area, near Stockbridge.
On Monday, Defra officials said a suspected foot-and-mouth case on the Hampshire-West Sussex border was a false alarm.
A 3km temporary control zone was set up around Slade Farm, near Rogate, on Sunday while Defra investigated the case.
The latest cases of foot-and-mouth in Surrey involved animals which were infected around the same time as the first cases, Chief Vet Debby Reynolds said.
The epidemiological report revealed the disease could have been spread to the fifth infected farm by the movement of people or vehicles, but not through animal-to-animal transmission or by airborne means.
Because the risk of the wider spread of foot-and-mouth was low, from 1530 BST on Tuesday some movement restrictions would be relaxed in England's low-risk areas, she said.
But a section of south-east England remains a risk area.
Farming leaders have called for the government to consider aid packages for those facing bankruptcy in the wake of movement restrictions brought in because of foot-and-mouth.
They say the restrictions mean farmers cannot buy and sell animals at a crucial time of year.
NFU president Peter Kendall has warned that farmers are facing "financial Armageddon" as a result of the crisis.
The latest case of foot-and-mouth is the fifth since the disease was confirmed on a farm near Egham, Surrey, on 12 September and the seventh in southern England since the beginning of August.
Some 1,800 animals have so far been slaughtered but some of the movement restrictions outside the current surveillance zone have been lifted.
An earlier outbreak in August, which affected two premises, was blamed on the virus escaping from leaking pipes at the nearby Pirbright laboratory site.
Government chief vet Debby Reynolds said farmers should remain vigilant for either bluetongue or the foot-and-mouth virus.