Ring-necked parakeets are an introduced species from India that are becoming very common in the areas around London. 6000 birds were once seen at Esher Rugby Club, roosting for the night. In Staines, they seemed to be much more common than magpies and pigeons. This is a male, which has a rose ring around the back of its neck that becomes black under the throat (another name for them is rose-ringed parakeet).
1: Virginia Water, Surrey, 27/12/2005.