Megrahi was greeted by Seif al-Islam el-Gadhafi, son of the Libyan leader
Opposition parties are increasing pressure on No 10 to explain whether the government played a role in the release of Abdelbaset Ali al-Megrahi.
The Lib Dems and Tories say "serious questions" need to be answered after Colonel Gaddafi's son claimed the case had been raised during trade talks.
The Foreign Office has strongly denied the claims that the Lockerbie bomber's release was part of any deal.
Meanwhile Col Gaddafi has praised his "friend" Gordon Brown.
Col Gaddafi has also singled out the Queen and Prince Andrew for encouraging the "courageous" Scottish Government.
The Scottish Government freed the terminally-ill 57-year-old on compassionate grounds on Thursday.
He needs to state on the record whether he, or any other member of his government, has at any time requested or suggested that Megrahi either be freed or transferred to a Libyan jail
Shadow foreign minister
In an interview with a Libyan TV station, Col Gaddafi's son Seif al-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.
The Conservative leader David Cameron has written to the prime minister asking him to give his opinion on the decision to free Megrahi.
Tory shadow foreign minister David Lidington said the comments by Col Gaddafi and his son meant it was essential Gordon Brown answered those questions.
"He needs to state on the record whether he, or any other member of his government, has at any time requested or suggested that Megrahi either be freed or transferred to a Libyan jail.
A crowd gathered to welcome Megrahi home to Libya
"It is very important, I think, for the reputation of our institutions of justice that it is made clear beyond any doubt that this was not connected with some political trade."
Liberal Democrat foreign affairs spokesman Ed Davey said although the Libyan leadership was not the most trustworthy source, he was "surprised" by Mr Brown's silence.
He said the British government still had questions to answer and the British and Scottish government appeared to be "dancing around each other, not criticising each other".
"I don't think any pressure was actually put from Westminster on Holyrood. I think they are willing partners in this," he told BBC Radio 4's Today programme.
He said the "new-found compassion" was welcome on one level, but "one does remember that there are billions of pounds of oil, gas, and bank contracts behind it".
"There is some evidence to suggest that, while there may not have been a written deal, we all know that diplomacy and trade operate in rather more subtle ways," he added.
However, the Foreign Office has insisted Megrahi's release had been a matter solely for the Scottish authorities.
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."
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".
Prime Minister Gordon Brown has so far made no comment, although it has emerged he wrote to Col Gaddafi to ask that Libya "act with sensitivity" in its welcome.
Former British ambassador to Libya, Sir Richard Dalton, said the "outstanding questions and silence" were not "serving the British interest well".