Theories as colourful as the bird itself abound about how exactly the UK got breeding colonies of exotic Ring-Necked Parakeets. That they were released into Carnaby Street to make it a brighter place by Jimmy Hendricks; they escaped from the set of the African Queen film when it was being filmed in London; then the slightly more boring and obvious one that they are simply descended from runaway pets.
The largest population is in London (especially Battersea Park, Richmond Park and Hampstead Heath), but breeding pairs can also be found in Highbury Park, in King's Heath, Birmingham. Although it can survive hard winters, it seems to only successfully breed and establish itself in cities, so is probably reliant on man for survival in this country.
The sexes of these bright green birds can be told apart quite easily. The male has a black neck ring and pink band on the nape of their neck, but the female (and immature male) lacks them.
They are quite noisey birds. To me they sound a little like two branches rubbing against each other and squeaking.