BBC correspondent Paul Rowley reports that: "The Tories believe that there is still mileage in the affair" (36")

MPs are to debate the arms-to-Africa affair as speculation grows that the attorney general will rule out prosecution of Sandline International for allegedly breaching the UN arms embargo on Sierra Leone.

The opposition are hoping to increase pressure on the British Government in a House of Commons debate chosen by the Conservatives.

Ex-civil servant tipped to head inquiry

The Foreign Secretary Robin Cook is also expected to name who will head the internal inquiry into allegations that Sandline were allowed to supply mercenaries and arms to Sierra Leone's ousted president Ahmed Tejan Kabbah earlier this year.

The Times has reported that Mr Cook will pick, a former senior civil servant Sir Thomas Legg QC, who was the Permanent Secretary at the Lord Chancellor's Department until March.

Mr Cook has said the inquiry will be headed by someone from outside the Foreign Office, once the Customs and Excise investigation has finished and cannot be prejudiced.

Customs has passed a report to the Attorney General John Morris who will decide if Sandline will face criminal charges. His decision is expected imminently.

Prosecution expected to be ruled out

Several newspapers have reported that Mr Morris is expected to decide against prosecution.

Michael Howard: seeking public inquiry

The Sunday Times quoted "senior Whitehall sources" as saying the prosecution case had been "fatally undermined" by evidence that shows "contacts and conversations" between diplomats and Sandline.

The sources are also said to believe any chance of a successful prosecution has been seriously damaged following the Prime Minister Tony Blair's attempts to dismiss the matter as overblown.

The Customs investigation began six weeks ago. It followed allegations that Sandline, headed by former Scots Guard, Colonel Tim Spicer, broke the UN embargo by supplying forces fighting to help reinstal President Kabbah.

In the end President Kabbah's civilian government was restored after the intervention of a Nigerian-led force, Ecomog.

Sandline denies sanctions-busting and has said it acted with the approval of the British Government - a claim strenuously denied by ministers.