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.

Sir Desmond Swayne has admitted to blacking up to go to a party as soul singer James Brown credit: Daily Echo/Solent News & Photo Agency

He said the photo was taken "years ago," adding: "It is definitely my wife. What does this add to what I have already said? Nothing.”

Asked if the man in the photograph was him, he replied: "It might be is all I can say. I can't deny it. I don't know the provenance of this photograph. It was years ago.”

Last week, Sir Desmond, MP for New Forest West, Hants who received a knighthood from Mr Cameron in 2016, revealed on his blog that he had “blacked up” for the party, insisting he would not apologise for his costume.

He even criticised the Canadian prime minister who was last month forced to apologise for wearing dark make-up at a party in 2001, saying: "I suspect that Justin Trudeau's cringing apology for blacking himself has done him rather more harm than the original offence."

He said on Monday: "All I said was that [Justin] Trudeau should not have apologised for what he did years ago, going to a private function.

"Arabian Nights as Aladdin. Blues Brothers as James Brown. Why do people take offence when none was intended?"

Sir Desmond, a former minister at the Department for International Development, wrote on his blog: "It was a themed Arabian Nights fancy-dress party for heaven's sake! It comes to something when you can't dress up as Aladdin without attracting the opprobrium of the 'great and good'."

He said Mr Trudeau should have written off the incident as a "bit of fun" and refused to apologise.

Justin Trudeau at an "Arabian Nights" gala in 2001 credit: West Point Grey Academy via CP

Sir Desmond added: "I once went to a Blues Brothers fancy-dress party as James Brown. I went to some trouble to be as authentic as possible. I can assure readers that I have no intention of apologising."

The former economics teacher and Army major admitted the only reason he would not black up again was the sheer effort it took to wash it off. "It's not a non-trivial exercise," he said.

Mrs Swayne, mother of the couple's three grown up children, on Monday declined to provide further details about the party, which is understood to have taken place several years ago.

She suggested the family was fed up with the furore surrounding her husband’s admission and “just wanted the whole thing to go away.”

Dawn Butler MP, Labour's shadow equalities secretary, said last week: "This is another example of a politician not even trying to understand the history of oppression and racism. The Tories need to explain what action will be taken."