Apart from Pot Bellied Pigs;

[xyzzyplugh]

Llamas, on farms these days. Ostriches too. The red-necked wallabies, near Leek in Staffordshire since the early 1940s Also pumas have been seen in U.K., most famously in Surrey. Know of any more unindigenous critters at large?.

[j2buttonsw]

They're milking buffalos in Bedfordshire nowerdays: apparently buffalo milk is creamier and lower in cholesterol.

[incitatus]

coypu and mink have been wild for years now. Rabbits are not native either, though its been a while since they arrived. Peacocks, caucasus pheasant, muntjac, even budgies.

[wildwood]

Feral cats.

[sddsddean]

Grey squirrels

[Gef]

Hamsters, Guinea pigs and gerbils?

[FredPuli]

The collared dove is found all over the UK nowadays but was only noted here first, in the South, in 1955. It is a native of North Arica which has settled progressively further north.Another recent bird is the ring-necked parakeet, from India, which exists in large colonies locally, established from cage birds escaping from 1960.