Trade with Libya played a "very big part" in Britain's decision to include the Lockerbie bomber in a prisoner transfer deal between the two countries, a senior British minister was quoted as telling a Saturday newspaper.

In an interview with the Daily Telegraph, Justice Secretary Jack Straw said his decision helped improve relations and pave the way for an oil contract signed by British oil major BP.

Prime Minister Gordon Brown has repeatedly said trade played no part in Britain's stance on the early release of Abdel Basset al-Megrahi, a move which angered the United States government.

Megrahi, 57, was freed early from a Scottish jail last month on humanitarian grounds because he has prostate cancer and officials said he may have only three months to live.

He was the only person convicted of the bombing of a Pan Am passenger jet over the Scottish town of Lockerbie that killed 270 people in 1988.

His early release and warm welcome home in Tripoli triggered an international row that Brown's political rivals said damaged relations between London and Washington.

Asked whether trade was a factor in his decision to include Megrahi in a prisoner swap deal with Libya, Straw told the newspaper: "Yes ... a very big part of that. I am 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."

The Scottish government, which has devolved powers for justice and other areas, freed Megrahi for compassionate reasons rather than using the prisoner transfer agreement.

However, ministers in London and Edinburgh have faced intense pressure from opposition politicians, the US government and some victims' relatives to explain whether trade played any role in the wider decision to release Megrahi.

On Wednesday, Brown said there was "no cover-up, no double-dealing, no deal on oil", while his effective deputy, Peter Mandelson, described suggestions that the release was linked to a trade deal as "offensive".

The British government has sought to distance itself from the decision, saying it was solely a matter for Scotland.

Documents released last week by the Scottish government showed Libyan officials had warned London the death of Megrahi in jail would have "catastrophic effects for the relationship between Libya and Britain".

British firms have become heavily involved in exploring for hydrocarbons in Libya after UN sanctions were lifted in 2003. – Reuters