We had (i havnt seen them for some years now) a small population of Green Parakeets in Longueville school woods in Peterborough, escapees i would think that built a small population...thats sadly gone now i assume.
There are tens of thousands of them in London and surrounding suburbs. They are a menace. Decimating fruit trees and driving out native birds. There is talk of a cull. And it's not before time.