Thousands of compatriots -- some waving Scottish flags -- greeted Abdelbaset Ali Mohmed al Megrahi last night, hours after President Barack Obama, who called his release a "mistake", pleaded with Libya to avoid making his return a victory celebration.

Megrahi’s freedom came after Scottish Justice Secretary Kenny MacAskill announced he was allowing the terminally-ill cancer patient to return home to die on compassionate grounds.

Frail and dressed in a white tracksuit and cap, 57-year-old Megrahi -- who was sentenced to 27 years for the murders of 270 people in 2001 -- walked unaided up the steps of a chartered Libyan jet at Glasgow airport, which left at 3.26pm for north Africa.

In a statement released as he made his journey to freedom, the former Libyan agent said: "This horrible ordeal is not ended by my return to Libya. It may never end for me until I die. Perhaps the only liberation for me will be death. And I say in the clearest possible terms, which I hope every person in every land will hear: all of this I have had to endure for something that I did not do."

Making one of the biggest decisions by a Scottish minister since devolution, Mr MacAskill had earlier said the dying Megrahi "now faces a sentence imposed by a higher power".

"It is one that no court, in any jurisdiction, in any land, could revoke or overrule. It is terminal, final and irrevocable. He is going to die," he told the world’s media.

Last night it was announced the Scottish Parliament is to be recalled early on Monday to debate the Megrahi decision, with pressure mounting on the Justice Secretary to justify his decision and amid questions about the effect Megrahi’s release will have on Scotland’s international standing. With the Libyan’s appeal now dropped, relatives of victims face not knowing the answers to many outstanding questions.

Pictures from Tripoli showed hundreds of people cheering Megrahi as he left the plane. A crowd also gathered in the city’s Green Square to apparently celebrate his release.

However, the Tripoli Post reported how people were shocked at his poor state of health.

The newspaper said: "Many are blaming the Scottish authorities for not taking care of Megrahi’s health while in prison and speculate that he was left, on purpose, to die of his cancer."

Pamela Dix, whose brother Peter died on the Pan Am jet that exploded above Lockerbie in 1988, condemned the celebrations. "I think a hero’s welcome is entirely inappropriate in the circumstances," she said.

A US relative, Susan Cohen, whose 20-year-old daughter, Theodora, died in the attack, said of his return: "I think it’s appalling, disgusting and so sickening I can hardly find words to describe it."

Mr Obama declared Megrahi should be placed under house arrest on his return to Libya.

"We have been in contact with the Scottish Government indicating that we objected to this," Mr Obama said in an interview from the White House on radio. "And we thought it was a mistake."

Mr Obama said his administration had called on Libya to ensure that Megrahi is "not welcomed back in some way, but instead should be under house arrest."

Megrahi left MHP Greenock yesterday in a convoy of police cars and prison vehicles.

Some onlookers shouted abuse as the convoy left, taking him on the 20-minute journey to Glasgow Airport where a private jet run

by the Afriqiyah airline was waiting to take him home to Libya. One of his five children was on board.

Megrahi was followed up the steps by Abdul Ati al-Obeidi, the Libyan minister and former ambassador.

Details of Megrahi’s personal plea for compassion were disclosed yesterday. "I am terminally ill. There is no prospect of my recovery," he told Mr MacAskill in a letter from jail. His plea was disclosed as private medical notes were also made public for the first time.

Last night, Sir Richard Dalton, who was British ambassador to Libya between 1999 and 2002, called the decision of Mr MacAskill to release the terminally-ill Megrahi "difficult" but "right".

He said: "Appalling though the atrocity was that led to the deaths of 270 people, there are not good reasons why anybody convicted of that crime should be excepted from normal rules which apply for considering release on compassionate grounds."

Jim Swire, who lost his

23-year-old daughter, Flora, in the atrocity and has been vocal in his belief in Megrahi’s innocence, praised the decision.

He told the BBC: "I don’t believe for a moment that this man was involved in the way that he was found to have been involved."