Lockerbie investigators have been given fresh assurances by Libya's interim Prime Minister that his government will co-operate "as a priority" as they pursue new lines of inquiry into the terrorist outrage.

Lord Advocate Frank Mulholland, QC, and Patrick Shearer, chief constable of Dumfries and Galloway Constabulary, the force investigating the 1988 bombing which claimed 270 lives, held talks in London yesterday with Abdurrahim El Keib.

It was their first since the death on Sunday of Abdelbaset Ali Mohmed al Megrahi, the man convicted of the bombing, from cancer more than 1000 days after his release from prison.

It comes after discussions in Tripoli last month between Mr El Keib, Mr Mulholland and Robert Mueller, the director of America's FBI, to discuss the investigation.

Mr El Keib was in London to meet Prime Minister David Cameron at Downing Street.

A Crown Office spokesman said: "Following the meeting with the Lord Advocate in Tripoli in April, the interim Libyan Prime Minister met the Lord Advocate and the chief constable of Dumfries and Galloway in London to discuss and re-affirm the commitment he gave to the Lord Advocate and the director of FBI in April that the new Libyan Government would co-operate with Scottish and US law enforcement in the investigation of ... the Lockerbie bombing.

"The Prime Minister asked for clarification on a number of issues relating to the conduct of the proposed investigation in Libya and the Lord Advocate has undertaken to provide this.

"The Prime Minister made it clear he recognised the seriousness of this crime, and following the clarification he would take this forward as a priority. As the investigation remains live, and in order to preserve the integrity of that investigation, it would not be appropriate to offer further comment."

Megrahi's death sparked renewed calls for investigators to pursue high-profile members of Colonel Gaddafi's now defunct regime.

Among people likely to be topping the interview list for prosecutors are

Moussa Koussa, the former head of Libya's external intelligence, and Abdullah al Senussi, Gaddafi's brother-in-law and former Libyan intelligence chief.

Both are believed to hold vital information about Libya's role in the plot to bomb Pan-Am flight 103, which exploded over Lockerbie killing all 259 on board and 11 people on the ground.

Yesterday First Minister Alex Salmond, responding to a request by Scottish LibDem leader Willie Rennie, rejected pleas for a Scottish public inquiry into the case.

Mr Rennie had claimed it was an opportunity "to shine a light" on the conduct of the Crown Office.

Prosecutors have been criticised over their handling of the case, with a report by the Scottish Criminal Cases Review Commission finding six separate grounds for a possible appeal against Megrahi's conviction.

Mr Salmond said: "As Willie Rennie should know, the relatives of Mr Megrahi have the ability, if they so choose, to go back to the Scottish Criminal Case Review Commission and seek further leave to appeal. That is the process which can be followed."

Meanwhile, a spokesman for Number 10 said: "The Prime Minister noted that Prime Minister El Keib had met with the Lord Advocate earlier in his visit regarding the Lockerbie case and hoped that progress would be made on outstanding questions."