Rose-ringed is most likely, there have been several reported on Avon birding recently.
An unexpected sighting this morning in woods to the south of Chewton Mendip. Attracted by loud squawking a parakeet high up looking very green/yellow in the morning sunlight. Larger than a kestrel with long pointed tail and too large I think for a monk parakeet. My best guess would be rose ringed parakeet but without binoculars difficult to be more specific.