A Conservative MP has questioned why his decision to “black up” for a party could be deemed offensive as the first picture emerged of him dressed up as James Brown.

Sir Desmond Swayne, 63, has admitted he “went to some trouble to be as authentic as possible” when he attended a Blues Brothers themed party as the American soul singer.

A photograph taken at the event shows the MP posing alongside his wife, Moira, who works as his secretary and was dressed as one of the Blues Brothers.

Sir Desmond, who in 2004 was appointed David Cameron's principal private secretary to help to drive through Tory modernisation, is almost unrecognisable in full “blackface” complete with black wig and sunglasses.

Mrs Swayne donned a classic Blues Brothers outfit of black suit and tie, sunglasses and a pork pie hat.

When shown the photograph by the Telegraph on Monday at the Tory Party Conference in Manchester, Sir Desmond quickly acknowledged it was his wife but was reluctant to confirm his own identity.