A lot of people class Blackcaps as a summer visitor but they are only a short distant migrant so a lot do hang around especially in the south of the country and if its not to cold there can be a lot of sightings generally. This can also happen to Chiffchaff's too, with the odd one or two staying about. I remember seeing one feeding in my garden in evergreen shrubs in January a few years ago. I was only about 3 feet away - best view of a chiffchaff i've ever had!
