Defending his part in the negotiations, Straw said: "I'm unapologetic about that ... Libya was a rogue state. We wanted to bring it back into the fold.
  
"And yes, that included trade because trade is an essential part  of it and subsequently there was the BP deal."

However, Straw's spokesman insisted that al-Megrahi's release was not agreed on because any possible transfer was always subject to a veto by the Scottish authorities.

Compassionate grounds

Al-Megrahi was the only person convicted of the 1988 bombing of Pan Am flight 103 over the Scottish town of Lockerbie which killed 270 people. He was released last month on compassionate grounds because he is  terminally ill.

Previously, London has  been forced to deny allegations that it struck a deal with Libya to free him in return for improved trade ties.

In depth

 Profile: Abdel Basset al-Megrahi
 Bomber's homecoming slammed
 Release prompts anger and relief
  Video: Al-Megrahi speaks out
  Video: Opinions divided over Lockerbie appeal
 Video: Lockerbie remembered
 Al-Megrahi statement in full

Gordon Brown, the British prime minister, announced on Thursday that "there was no conspiracy, no cover-up, no double dealing, no deal on oil, no attempt to instruct Scottish ministers, no private assurances by me to Colonel Gaddafi".

But documents released this week show that Straw used the possible release of the prisoner when talks on the ratification of a huge oil deal  between BP and Libya had become bogged down.

The $900 million deal was ratified in January 2008 shortly after Straw's change of  strategy.

But Musa Kusa, Libya's foreign minister, said in an interview on Saturday that trade had nothing to do with al-Megrahi's release.

"You should not do an injustice to the British government," he  told British newspaper The Times from Tripoli. "It was nothing to do with trade. If we wished to bargain we  would have done it a long time ago."

BP said Friday it had lobbied Britain to speed up the agreement with Libya to improve business relations, but denied pressing for al-Megrahi to be released.