British Prime Minister David Cameron made an unexpected visit to the Libyan capital of Tripoli on Thursday and announced that Scottish police officers will travel to the North African nation to investigate what are believed to be new leads the Lockerbie bombing.

He also held bilateral talks to explore what support and expertise Britain can offer to Libya to strengthen its security and defeat terrorism.

Cameron told a press conference in Tripoli he was "delighted" that police would be able to visit Libya and "look into the issues" around the 1988 bombing of Pan Am Flight 103 over the Scottish town. The attack killed 270 people.

The death last spring of Abdel Basset al-Megrahi — a former Libyan intelligence agent and the only man convicted over the Lockerbie bombing — renewed pleas from victims' relatives for further investigation of the bombing. After the 2011 fall of dictator Moammar Gaddafi, Britain asked Libya's new rulers to help fully investigate.

In September last year, the Crown Office requested new hearings be held in Malta, where the Lockerbie bomb supposedly began its fateful journey, looking into the actions of Megrahi, Fhimah and the Libyan intelligence service.  Those hearings have taken place, but they have been held behind closed doors.

Scottish police will head to Libya within weeks to launch new investigations into the Lockerbie bombing, after Libyan officials granted Dumfries and Galloway detectives permission to enter the country for the first time since the fall of Muammar Gaddafi in October 2011.

“I am delighted that the Dumfries and Galloway Police team will be able to visit your country to look into the issues around the Lockerbie bombing,” the Prime Minister said in Tripoli.

Lord Advocate, Frank Mulholland QC, has already travelled to Libya, along with US investigators, as the Crown Office continues to see Scotland’s worst ever mass murder as a live case.

The agreement to allow police to visit the home country of al-Megrahi – who 12 years ago this week became the only person ever convicted of the 1988 atrocity – has been welcomed by the Crown Office and First Minister Alex Salmond.

Dumfries and Galloway Constabulary have remained tight-lipped over who they want to speak to, and what lines of inquiry they will pursue, according to British press reports.

A spokesman for the force said: “Dumfries and Galloway Constabulary welcomes the support of the Libyan authorities for the ongoing investigation. Travel details and dates cannot be released for security reasons, and to protect the integrity of the investigation.”

Officers are expected to travel in March and their focus is likely to be on members of the former administration and, in particular, of the Libyan intelligence services who worked under Gaddafi.

The Crown Office is still investigating Al Amin Khalifa Fhimah, Megrahi’s co-accused and fellow Libyan, who was acquitted at Camp Zeist.

Former FBI assistant director Buck Revell, who oversaw that agency’s Lockerbie investigation until 1991, told The Scotsman newspaper this week: “The two individuals initially charged were not the only people involved. So there’s no doubt that this was approved by Gaddafi and everyone in the chain of command below him.

“There are documents, witnesses and other evidence that they can obtain in the intelligence service, or the military, or from other individuals involved in support organisations.

“I expect much, if not most, of it has been destroyed, but maybe some was saved.”

He added: “The crime itself is such that I don’t believe this case should ever be closed.”

However, British relatives of victims of the bombing of the Pan Am flight 103 who have protested that Megrahi was innocent are sceptical of what might be achieved in Libya.

Mr Mulholland told the families that he intended to send police to the country in February last year, two months before he himself visited.

Dr Jim Swire, whose daughter Flora, 23, died in the bombing, said: “He told us how he was going to send officers to Tripoli to try and find out more.

“Anyone who tries to gather evidence from modern day Libya should be careful. The interim government wishes to place every conceivable blame on the Gaddafi administration.”

Reverend John Mosey, who lost his daughter, Helga, 19, in the bombing, added: “I would be extremely sceptical about what could be found in those blasted and burned out offices.

“The former regime probably shredded anything it had.”

The campaign group Justice for Megrahi, which wants an independent inquiry into the conviction, was scathing about the continued focus on Libya.

“As far as I am concerned, the conviction was a gross miscarriage of justice and the efforts the police and Crown Office are making to locate other Libyans who may have colluded in the bringing down of Pan Am flight 103 amount to little more than eye-wash,” said group secretary Robert Forrester.

But the Crown Office remains convinced Libya is key to their investigation. One man widely believed to know the secrets of the Gaddafi government is Moussa Koussa, who briefly sought refuge in the UK, following the Libyan revolution.

John Ashton, author of ‘Megrahi: You Are My Jury’, and former FBI agent Richard Marquise – two men with very different views on whether Megrahi was guilty – have both said investigations should focus on the former intelligence chief.

In his book, Mr Ashton argued Megrahi could not have been the bomber because the timer used in the explosion contained a different coating to circuit boards sold to Libya.

Abdallah Senussi, Gaddafi’s brother-in-law and head of the intelligence services, who was Megrahi’s immediate boss, is another man the FBI have looked at in connection with Lockerbie.

Other potential suspects include Saeed Rashid, whom an FBI report previously claimed “managed a sustained Libyan effort to conduct terrorist attacks against US interests since the early-1980s”, and Izz Aldin Hinshiri, who was suspected of buying the trigger for the Lockerbie bomb.

Unlike many of the British families, US relatives have never doubted Megrahi’s guilt, but believe he did not act alone.  Rosemary Wolfe, 71, of Myrtle Beach, in South Carolina, lost her step-daughter Miriam, 20, in the bombing.

“It’s about time they opened up their files and let us talk to their people,” she said. “It would certainly be good to get some of the truth and some measure of justice after all these years.”