LONDON  —  Trade and oil considerations played a big part in the decision to include the Lockerbie bomber in a prisoner transfer agreement between Britain and Libya, a senior British official said in an interview published Saturday.

Justice Secretary Jack Straw said trade, particularly a deal for oil company BP PLC, was “a very big part” of the 2007 negotiations that led to the prisoner deal. The agreement was part of a wider warming of relations between London and Tripoli.

“Libya was a rogue state,” Straw was quoted as saying by The Daily Telegraph newspaper. “We wanted to bring it back into the fold and trade is an essential part of it — and subsequently there was the BP deal.”

The British government has faced intense criticism over the release of Abdel Baset al-Megrahi, a Libyan convicted in the 1988 bombing of a Pan Am airliner over Lockerbie, Scotland. The attack killed 259 people aboard the plane, most of them American, and 11 on the ground.

Last month Scottish officials freed al-Megrahi, 57, on compassionate grounds because he is dying of prostate cancer.

Although he was not released under the prisoner transfer agreement, opposition politicians, and many victims’ families, claim business considerations influenced the decision to free him.

On Wednesday, Prime Minister Gordon Brown insisted there was “no conspiracy, no cover up, no double dealing, no deal on oil” over the bomber’s release.

But officials admit the prisoner transfer agreement was part of a wider set of negotiations aimed at bringing Libya in from the international cold, and improving British trade prospects with the oil-rich nation.

Documents released by the government show Straw had originally tried to ensure that al-Megrahi was exempted from any prisoner deal with Libya, but in December 2007 he changed his mind. He wrote in a letter to his Scottish counterpart that “wider negotiations with the Libyans are reaching a critical stage” and a blanket agreement was in “the overwhelming interests for the United Kingdom.”

Soon after, Libya ratified a $900 million oil exploration deal with BP. The oil company acknowledged Friday that it had urged the government to sign the prisoner transfer deal, but insisted it had not singled out al-Megrahi as part of the discussion.

Straw said Brown had not been involved in negotiations over the prisoner agreement.

“I certainly didn’t talk to the PM,” he was quoted as saying. “There is no paper trail to suggest he was involved at all.”