It is estimated 100 of the animals, which originally escaped from farm enclosures, are living on the borders of Kent and East Sussex. The study was started after farmers reported that the animals were causing agricultural damage.
The boar population, which also includes between 12 and 20 animals living in Dorset, are breeding in the wild, the study disclosed.
The animals have caused damage on pasture land and to cereal crops in Kent and East Sussex and on pasture land in Dorset. Farmers in Kent and East Sussex have also reported predation on lambs.
Elliot Morley, the Countryside minister, said: "We commissioned this assessment ... to identify the effects they are having in the countryside. In the light of comments received the ministry will consider what, if any, action would be appropriate ... We shall ... be carrying out a fuller assessment of the risks to animal health from escaped wild boar." The boar are not thought to pose a risk to human safety but confrontations between the animals and the public and farmers have occurred, according to the report.
Wild boar have also been involved in road accidents in Kent, East Sussex and Dorset. There have been a number of sightings of sows with young and animals in Dorset may also be breeding: accounts were reported of sows with piglets. The ministry said it is impossible to establish where the boar originally escaped from, as they carry no identification marks and ownership cannot be determined.
In England they are kept in farms, wildlife parks and private collections. Wild-boar farming is relatively new; 40 farms are registered with the British Wild Boar Association.
They may only be kept under licence; it an offence to release wild boar or to allow them to escape.Reuse content