In the UK, this unusually coloured (male) butterfly is restricted to central southern English woodland (6,7)

I believe the answer is:

purple emperor

(Other definitions for purple emperor that I've seen before include "Butterfly (appropriately coloured)" , "Flyer" , "Insect" , "One flapping about" , "European butterfly" .)

I've seen this clue in The Sunday Times and The Times.

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