In a chilling account of the Gaddafi regime, David Pratt refers to the congratulatory correspondence sent by the MI6 chief officer, Sir Mark Allen, to Moussa Koussa, head of Libyan intelligence (1994-2009) (Rendition, torture, MI6 and the secrets of Libya's gulag, The world, June 12).

The recipient of these letters, which proved that MI6 had been complicit in the abduction and extradition of Libyan dissidents to Tripoli to face years of torture and probable death, defected during the overthrow of colonel Gaddafi and fled to Britain in March 2011. He was immediately taken into police custody, whereupon the then foreign secretary, William Hague, appeared on television to announce that Koussa would be interrogated by MI6.

Crucially, Koussa was also to be interviewed by Scottish prosecutors in relation to Lockerbie, leading to the possibility of a breakthrough, much trumpeted by Hague. Koussa, a close friend of Gaddafi's since their student days, had, after all, been instrumental in the eventual handover of Al-Megrahi for trial, while welcoming the latter's compassionate release nine years later. There followed a deafening silence on the outcome of Koussa's interrogation, and he was not heard of again until five months later when a Channel 4 camera crew tracked him down to a hotel foyer in Qatar. Had he been allowed to leave London with impunity?

If, in March 2011, William Hague (now Baron of Richmond) and the Scottish prosecutors had good intentions to discover the truth about Lockerbie, and were not simply presiding over a charade, then they owe an explanation and an apology to the families of the Lockerbie victims still in pursuit of justice. Absolutely no-one believes that Moussa Koussa had no story to tell.

John S Laverie

Edinburgh