The Liberal Democrats will on Thursday attack the government’s move to abandon the Serious Fraud Office investigation into BAE Systems’ dealings in Saudi Arabia, in a House of Lords debate.

They will call for the role of the attorney-general to be made more independent, question his claim that no pressure was put on Robert Wardle, the SFO director, to come to the decision and dispute the government’s assessment that the Saudis would have withdrawn co-operation on intelligence and security had the inquiry continued.