One of Colonel Gaddafi's sons was offered police protection in the UK in 2004 after intelligence was uncovered about an apparent plot to have him killed.

Officers from Scotland Yard's special branch spoke to Saif al-Islam Gaddafi and reassured him that steps were being taken to ensure his safety. He was also put on the police's "at risk" register.

The details of the threat to Gaddafi's 38-year-old son, and the efforts that Scotland Yard and MI5 made to look after him, are contained in documents found in Tripoli since the fall of the old regime.

At the time of the plot in early 2004, Saif Gaddafi was living in London. Britain and the US were at pains to ensure that nothing upset Libya's return into the international community.

Like his father, Saif is now on the run in Libya, hunted by the National Transitional Council and wanted by the international criminal court accused of crimes against humanity, murder and torture. He has often been the defiant face of those forces still loyal to his father.

Once a guest of Prince Andrew at Buckingham Palace, he enjoyed friendships with leading British politicians, and was even offered help in his PhD at the London School of Economics by the former prime minister, Tony Blair.

In among the hundreds of documents left abandoned when Tripoli fell into the hands of rebel forces were two relating to Saif al-Islam Gaddafi. Although it is impossible to be sure the files are genuine, there has been no attempt to challenge their authenticity by western governments or intelligence services.

One memo, dated January 2004, and for the attention of Sadeq Krima, head of Libya's international relations department, is titled: "Threat to Saif al-Islam al-Gaddafi". It may have come from the CIA.

It says: "We are in the process of tracing the names in the report passed to us regarding the threat … and will respond when our traces are complete. In the process of tracing the names in the report … we note that the attempt may take place in either the UK or France."

A second note, sent two weeks later, adds: "Neither we or the British security service have any traces on the individuals named. The report has been passed to the Metropolitan police special branch and Saif al-Islam has been placed on their 'at risk' register.

"The police have visited him to discuss the threat with him and he appears to be content with the measures being taken."

The letter also seeks help from the Libyans to identify those behind the plot.

"Are these individuals connected to any particular extremist group? Why have they chosen Saif al-Islam as their target? Are they in fact Libyan nationals? Where are they currently based? What form will the attack take?"

It is not clear what "measures" were offered to Gaddafi, but special branch is Scotland Yard's elite unit with responsibility for the protection of the royal family and other foreign dignitaries.

Earlier this week, it emerged that the documents found in Tripoli contained details of how two Libyan dissidents were taken back to their home country against their will. One of those returned to Libya was Abdul Hakim Balhaj, a rebel commander who is now in charge of security in Tripoli.

He has said he was repeatedly tortured in custody and demanded an apology from the British and American governments for their complicity in his rendition.

Balhaj was a leading member of the Libyan Islamic Fighting Group (LIFG), as was Abu Munthir, another dissident who was extradited back to Tripoli. Documents found last week suggest that Munthir was wanted by the Americans and the British because of his alleged links to al-Qaida.

In what may have been provided as supporting evidence for his extradition from Hong Kong back to Tripoli, the Libyans provided papers which claimed Munthir was an "intimate" of Osama bin Laden.

They alleged that Munthir moved with Bin Laden to Sudan, and had flown to the UK in the mid-1990s. Other documents show how the British and American intelligence agencies were desperate for any information about members of the LIFG, a group which – at the time – they feared had links to Islamic extremists.

In one set of papers, the CIA asked the Libyans to pose 59 separate questions to a member of the LIFG they had in custody.

Libya also provided the details it had of 130 dissidents, 115 of whom it accused of being members of the LIFG. Fifty-nine of the people named were said to be living in the UK. The details of the men were put on Interpol's Restricted/Fusion Taskforce website.

Scotland Yard refused to comment on the threat to Gaddafi.