The man convicted of killing 270 people aboard a transatlantic airliner in 1988 said he would present the evidence through lawyers in Scotland and ask the British and Scottish communities to "be the jury".
He said he was "very, very happy" to be free.
"This was my hope and wish - to be back with my family before I pass away. I always believed I would come back if justice prevailed."
Colonel Gaddafi's son had labelled Megrahi's release a "victory".
In an interview with a Libyan station, Mr Islam reportedly claimed that the Megrahi issue had been raised repeatedly by Britain's former prime minister Tony Blair.
"In all commercial contracts, for oil and gas with Britain, (Megrahi) was always on the negotiating table," Mr Islam said told Libya's Al Mutawassit channel.
Mr Blair visited Libya in May 2007, during which UK energy giant BP signed a $900m (£540m) exploration deal.
However, the Foreign Office insisted Megrahi's release had been a matter solely for the Scottish authorities.
I never for a minute thought that it was just a question of compassionate release and the humanity and compassion of the Scots
Rosemary Wolfe Stepmother of bombing victim
A spokesman said: "No deal has been made between the UK government and the Libyan government in relation to Megrahi and any commercial interests in the country."
UK Foreign Secretary David Miliband earlier rejected suggestions the UK pushed for Megrahi's release to improve relations as "a slur on both myself and the government".
But Rosemary Wolfe, whose stepdaughter died in the bombing, said she was not surprised by claims that the release was part of a trade deal with Britain.
She told the BBC: "I never for a minute thought that it was just a question of compassionate release and the humanity and compassion of the Scots.
"What surprises me is that Gaddafi's son would have come out with this kind of a statement."
A former British ambassador to Libya, Sir Richard Dalton, said the UK government faced scrutiny over the circumstances surrounding Megrahi's release.
"There are a number of outstanding questions and silence I don't think is serving the British interest well," he said. "In my view it was not naivety, nor was it opportunism."
"There are honourable answers to the questions being posed and it is time, I think, for the British government to be more forthcoming in support of what the Scots have done."
Separately, the Foreign Office was unable to confirm whether a planned trip to Libya by the Duke of York in September would be cancelled.
A spokeswoman said an official invitation to the British government from Libya had not yet been received.
However, it is believed any visit by a member of the Royal Family is unlikely to go ahead in light of the furore surrounding Megrahi's return.
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