The National Pig Association (NPA) has warned that members of the public who keep such pigs could unwittingly be perpetuating serious animal welfare problems.

Some miniature pig lines were originally developed for medical research and can therefore carry genetic mutations responsible for deformities linked to animal dwarfism, such as deformed skulls and weak limbs.

Other lines of micro-pig have been developed by successively breeding from litter runts, which can lead to expensive vet bills caused by genetic weaknesses and susceptibilities, including walking difficulties and obesity.

Continued breeding of micro-pigs may compromise animal welfare and should not be encouraged, the NPA has said.

Pigs generally do not make good house pets because they are predisposed to root and chew, so they can be destructive if kept in a house or smart town garden.

The NPA warned the pigs also pose a risk to the nation's commercial pig herd, as micro-pigs can catch and spread diseases such as foot and mouth, but in many cases may be harder to trace as some owners may not be aware of the legal requirement to register them.

A further risk for unsuspecting buyers is they may be sold what appears to be a micro-pig, but is in fact just a small pig which in time will grow to 150-200 kilos.