London has a massive population of feral parakeets, they can survive quite far north of the weather is mild. London is basically an urban forest so that does help.

https://en.wikipedia.org/wiki/Feral_parakeets_in_Great_Brita...

I have lots of them showing up outside my office window... E.g. [1]

But the occasional survival eventually leading to a breeding population doesn't mean the odds of survival for released/escaped birds who have grown up in captivity isn't really low.

[1] https://m.galaxybound.com/@vidar/115909920534715199

Liverpool too. Big flock of them in Sefton park in the south of the city. Pretty nice to see actually!