Oliver Miles, a former British ambassador to Libya, said: “Mr Blair is clearly using his Downing Street contacts to further his business interests.”

The meetings took place at a time of intense negotiations with Gaddafi’s regime over the release of Megrahi, convicted of murdering 270 people in the single biggest terrorist atrocity committed in Britain.

The bomber, who has cancer, was finally released in August 2009 after doctors wrongly gave him just three months to live.

Mr Blair has always denied involvement in Megrahi’s release – saying it was a decision taken by the Scottish Executive alone. Last night a spokesman admitted Megrahi’s release was raised by Gaddafi.

Mr Blair has refused to make public the full extent of his meetings in Libya since leaving office in June 2007.

The emails and letters – between Mr Blair’s office, the British ambassador in Tripoli and the Libyan ambassador in London – raise concern over possible conflicts of interest regarding his varied roles as Middle East peace envoy, philanthropist and business consultant.

The documents will also add fuel to suggestions made last year by Gaddafi’s son, Saif, that Mr Blair had advisory links to the Libyan government and the Libyan Investment Authority, which controls a £41 billion fund.

Mr Blair has categorically denied the connection.

The documents outline arrangements for the trips in 2008 and 2009. Mr Blair also held a further private meeting with Gaddafi in June 2010 after Megrahi’s release.

In both 2008 and 2009, the documents show Mr Blair negotiated to fly to the Libyan capital from Sierra Leone, in a jet provided by Gaddafi.

In 2008, Mr Blair, having met Gaddafi, arranged to fly on to Luton on a Libyan jet.

The first letter was sent on notepaper headed Office of the Quartet Representative, Mr Blair’s title as a Middle East peace envoy, which he took up after resigning as prime minister in June 2007.

The letter, written on June 2, 2008, was sent to Omar Jelban, Libya’s ambassador to Britain. It was written by Gavin Mackay, who was based at Mr Blair’s London office in Grosvenor Square, and stated: “Let me begin my [sic] saying that Mr Blair is delighted that The Leader is likely to be able to see him during the afternoon of 10 June and he is most grateful that the Libyan authorities have kindly offered an aircraft to take him from Freetown to Tripoli and back to London.”

The letter continues: “In addition to a call on The Leader, he [Blair] would welcome the opportunity to have a meeting with Deputy Prime Minister and Assistant Secretary Dr Abd-al-Hafid Mahm-jud al-Zulaytini, who he has met in the past.” Mr Zulaytini was one of Libya’s most powerful men and a former chairman of the state-owned National Oil Company.

Details of the 2009 meeting are contained in an exchange of emails between Victoria Gould, who was Mr Blair’s events organiser, and Sir Vincent Fean, the former British ambassador to Libya. The correspondence shows Tim Collins, a billionaire friend of Mr Blair, attended the meeting with Gaddafi.

Miss Gould wrote to Sir Vincent on March 31 to say that an audience with Gaddafi was “looking positive”, adding: “If we were able to stay at the Residence I know TB would be really grateful (as would we all).”

The email gives flight details and a plea that the group “need wheels” to return to the airport in Tripoli in time for the flight back to London. Three hours later, Sir Vincent replied: “Just to confirm the residence is at your disposal.”

A week later on April 7, 2009, Miss Gould confirms the visit is going ahead. “We have asked the Libyans to collect us from Sierra Leone and bring us to Libya,” wrote Miss Gould.

She then provides a list of people staying with the ambassador – including herself, Mr Blair, and Catherine Rimmer, a former Downing Street adviser and now Mr Blair’s strategic director.

The rest of the group, including several police officers, Mr Collins – described by Miss Gould as a “very successful investor and philanthropist” — and Mr Blair’s official spokesman Matthew Doyle stayed at the Corinthia Hotel, where rooms typically cost about £300 a night.

The email goes on: “In terms of calls, if you could note that TB would like to do the following: a meeting with the Leader (partly 1:1 and partly with Tim Collins) Then the following meetings with TB starting them on his own and then Tim Collins joining: Abdulhafeed Zlitney, Mohammed Lyas, Africa development Fund (incl Zarti?)” Mr Zlitney is thought to be an alternative spelling of Mr Zulaytini; Mr Lyas refers to Mohammed Layas, the head of the Libyan Investment Authority; while “Zarti” is thought to be Mustafa Zarti, the deputy head of the investment authority.

According to the email, Mr Doyle and four police officers flew back to London on a scheduled British Airways flight while the rest of the party left on Mr Collins’ ‘private charter’. Mr Collins had flown separately from the US.

The 2009 meeting occurred a day after Britain signed a prisoner transfer agreement with Libya, just one of several steps paving the way for Megrahi’s release from jail.

In June 2008, there was already growing clamour in Libya for Megrahi’s release.

Mr Blair has made a fortune since leaving Downing Street through speaking engagements and consultancy deals largely set up in the Middle East and the US. His personal wealth is estimated at anywhere between £20 million and £60  million.

He is also paid about £2.5 million a year by JP Morgan, a US investment bank which has a number of business interests in Libya. A spokesman for Mr Blair said last night: “The subjects of the conversations during Mr Blair’s occasional visits was primarily Africa, as Libya was for a time head of the African Union; but also the Middle East and how Libya should reform and open up.

“Of course the Libyans, as they always did, raised Megrahi. Mr Blair explained, as he always did, in office and out of it, that it was not a decision for the UK government but for the Scottish Executive.”

The spokesman added: “Tim Collins accompanied Mr Blair on one visit. No business deals of any nature were discussed.

“At the time, governments around the world were engaging with Libya.

“There was therefore at that time no reason whatsoever for not continuing to engage with him, especially since Mr Blair in office had been responsible for getting Gaddafi to give up his chemical and nuclear weapons programme and renounce terrorism.

“As we have made clear many times before, Tony Blair has never had any role, either formal or informal, paid or unpaid, with the Libyan Investment Authority or the Government of Libya and he has no commercial relationship with any Libyan company or entity.”

A source close to Mr Blair said he had never used Gaddafi’s personal jet but had used a Libyan government plane.

A spokesman for Mr Collins, who made his fortune in Japan, said last night: “Tim was asked to go by Tony Blair in his position as a trustee of Mr Blair’s US faith foundation. Tim had no intention of doing any business with Gaddafi.”

Sources in Libya said Gaddafi had discussed with Mr Collins opening beach resorts along the Libyan coast but that Mr Collins had dismissed the idea because the Libyans would not sanction the sale of alcohol or gambling at the resorts.

The source said: “Blair and Collins didn’t get anything for their faith foundation and Mr Collins made it clear he didn’t want to do business in Libya and considered Gaddafi crazy.”