As something of an ornithologist, I was amazed to see the Ring Necked Parakeet included in a book of bird visitors to British Gardens that was published in the nineties. I can remember looking into how they arrived in the country at the time and my findings matched what the RSPB website says today - it's impossible to pin down exactly how it happened, but it seems to have taken place sometime in the seventies.
I notice that the RSPB's page on the bird says that they are still limited to the south east of England and that "Birds are regularly reported elsewhere in Britain, and are likely to be local escapees.".
https://www.rspb.org.uk/our-work/pol...ked-parakeets/
https://www.rspb.org.uk/birds-and-wi...cked-parakeet/