AMERICAN relatives of the Lockerbie bombing victims have condemned the British government for secretly advising Libya on how to secure the release of the bomber.

But they appear resigned to the possibility that commercial interests had driven the decision.

''It's not hindsight, but I remember everyone thinking at the time that it had to do with oil,'' said Eileen Monetti of New Jersey, whose 20-year-old son, Rick, was among the 259 people killed on Pan Am flight 103. Eleven people died on the ground.

Documents obtained by WikiLeaks show that a Foreign Office minister sent Libyan officials detailed advice on how to use Abdelbaset al-Megrahi's cancer diagnosis to ensure he was freed from prison on compassionate grounds. Prince Andrew is also said to have played a role in encouraging his release.

The documents undermine claims by the then Labour government that it was not complicit in Megrahi's release and that the decision was taken by the Scottish executive alone.

Jane Schultz, of Centre Valley, Pennsylvania, said: ''It just reeks of everything bad in the world.''

Her son, Thomas, also 20, was returning from study in London on the ill-fated flight.

''I guess there's a part of me that knows there's nothing more that can be done … it all comes down to oil. 'We won't give you oil unless you give our terrorist back'.''

The revelations will add to US pressure on British Prime Minister David Cameron to release all internal documents detailing Britain's role in the affair. Mr Cameron has pledged to release the information.

Megrahi, a Libyan intelligence officer, was imprisoned in 2001 for life after being found guilty of bombing flight 103 over the Scottish town of Lockerbie in 1988.

For several years, the Libyans pressed for him to be returned under a prisoner transfer agreement that was being negotiated. According to US officials, Tony Blair was suspected of securing trade deals after agreeing to include Megrahi in the agreement.

In October 2008, Megrahi was diagnosed with cancer. Within a week of the diagnosis, Bill Rammell, a junior Foreign Office minister, had written to his Libyan counterpart advising him how this could be used as grounds for compassionate release.

Rob Dixon, a Foreign Office official, met the US ambassador to brief him on the letter.

Mr Dixon disclosed that Jack Straw, the justice secretary at the time, had spoken to Alex Salmond, the Scottish first minister, which had led officials to believe that the terrorist would be released.

Documents disclose that the Qatari government, one of the richest in the world, became involved in the effort to secure Megrahi's release. The Americans thought that the Qataris may have offered financial incentives to the Scottish executive, along with Libyan offers.

After Megrahi was released in August 2009, an American document records comments by Mr Gaddafi suggesting that Prince Andrew, Britain's special trade envoy, may have played a role.

The document records: ''He [Gaddafi] went on to thank his 'friend [Gordon] Brown', the British prime minister, his government, Queen Elizabeth, and Prince Andrew, who 'against all odds encouraged this brave decision'. [He] noted that the UK efforts would positively affect 'exchange' between the two countries.''

Despite the diagnosis, Megrahi is still alive in Libya.

Libya has large reserves of gas and more than 40 billion barrels of untapped oil and production is increasing.

TELEGRAPH, with SIMON MANN