Louis Susman, 71, a former banker from Chicago and one of Barack Obama’s key backers during the presidential campaign, said the special relationship was like a marriage in which there were disagreements.

He said: “This was a spat, a case where friends can disagree. Do I think it has diminished the relationship on a long-term basis? Absolutely not.”

Mr Susman dismissed threats of a boycott of British goods in wake of the decision by Scottish Justice Secretary Kenny MacAskill, adding: “I will continue to drink Scotch whisky, I love Scottish golf courses and we buy Scottish sweaters.”

The latest reports before Christmas about 53-year-old Abdelbaset Ali Mohmed al Megrahi were that his condition was worsening. Mr MacAskill took his decision to free the Libyan on compassionate grounds in August in the light of claims that al Megrahi, who has terminal prostate cancer, had three months to live.

On the “special relationship”, Mr Susman insisted it was “stronger than ever”. He added: “President Obama considers Britain our most important ally; they’re our best friend. He constantly expresses to myself and others and asks us to do it, our appreciation of the sacrifice you are making in Afghanistan and the bravery and courage of your soldiers, who are dying alongside our soldiers.”

Louis Susman