Libya has been courted by government ministers and Foreign Office mandarins on a dozen or more occasions in pursuit of lucrative oil and gas contracts.

Documents obtained by the Observer show ministers and senior civil servants met Shell to discuss the company's oil interests in Libya on at least 11 occasions and perhaps as many as 26 times in less than four years.

Foreign secretary David Miliband and the former Labour leader Lord Kinnock were involved in the meetings with Shell about its business in Libya or Egypt.

The revelations, showing that the government invested large amounts of political capital in securing North African oil, lend weight to claims that commercial interest lay behind last week's decision to release the Lockerbie bomber, Abdelbaset al-Megrahi, from jail in Scotland to receive a hero's welcome in Libya.

Gordon Brown has insisted that Whitehall had no involvement in the release, but critics of the government say the information obtained by the non-governmental organisation, Platform, via a Freedom of Information Act request, raises fresh questions. "These documents show the deep and long-term foreign policy backing provided by the British government to Shell in its efforts to break into Libya. Corporate executives have easy access to the highest level of Whitehall, while democracy advocates and social movements remain shut out on the street," said Mika Minio-Paluello, a campaigner with Platform.

"Yet again, the Foreign Office has prioritised securing new oil reserves for private corporations over human rights, the environment or democracy. Foreign policy should represent people's interests, not corporate interests. As a first step, the government must open its files and disclose the true level of oil influence on government decision-making."

Shell was one of the first western oil companies to re-enter Libya – one of the world's biggest potential oil sources – following the end of United Nations sanctions and a commitment from leader Colonel Muammar Gaddafi to turn his back on funding terrorism and pursuing nuclear weapons.

A deal was signed by Shell on 25 March 2004 covering the establishment of a "long-term strategic partnership" between the oil company and the local state-owned energy group. It was penned during a ground-breaking visit by the then prime minister, Tony Blair, and was followed up by meetings during July between Shell and foreign minister Baroness Symons and then the foreign secretary at the time, Jack Straw.

In October, Malcolm Brinded, the head of exploration at Shell who signed the deal to explore for oil and redevelop a gas export terminal in Libya, met another foreign minister, Douglas Alexander, with a particular focus on trade. In February 2005, Kinnock was involved in a reception at which Shell was present and North African oil interests were raised.

Anthony Layden, the British ambassador to Libya, was engaged in a series of meetings during April of the same year with Shell in Tripoli. Miliband met with Brinded in October of that year.

Shell said last night it had "no comment" to make on any discussions it had held with British ministers or other government officials about Libya, and the Foreign Office was unable to discuss these meetings.

But a government spokeswoman denied British oil interests played any part in the release of the Lockerbie bomber. She said: "There is no deal – all decisions relating to Megrahi's case were exclusively for Scottish ministers, the Crown Office in Scotland and the Scottish judicial authorities. No deal has been made between the UK government and Libya in relation to Megrahi and any commercial interests in the country."

Yesterday Megrahi backed calls for a public inquiry into the atrocity. He said he was determined to clear his name and that an inquiry would help families of the victims know the truth.

Megrahi said he would help Dr Jim Swire, whose 23-year-old daughter Flora died in the disaster and who has frequently called for a full public inquiry, by handing over all the documents in his possession.

• This article was amended on Sunday 30 August 2009. In the article above, we were mistakenly informed by the Foreign Office that the Prince of Wales had visited Libya in 2006. This is not the case. This has been corrected.