Ring-necked parakeets in Swansea?

My son, who lives in Brynmill, Swansea, phoned last week to say there was a 'green parrot' sitting on a branch of a tree in his next door neighbour's garden.  I suggested it might be a ring necked parakeet, which I have often seen in the South of England (Kent, Sussex) but never in Wales.  He looked at pictures on the RSPB website and confirmed this was the bird he saw.  A few days later, his flatmate also saw it (or another one) in the same area.  According to the RSPB website it is reasonably common in the South of England.  My (and my son's) question - could this have been a wild bird, migrated from England?  Are they spreading across the UK?  Or was this an escapee from an aviary or private home?  I've asked several friends who live in Swansea, and none of them have seen one.

Adar am byth!