Inquiry was set up to find if British officials acted illegally in the snatch

If claims proved, it will show one security arm of State spied on another

The Met commissioner Sir Bernard Hogan-Howe (pictured), set out claims detectives were bugged by intelligence agencies whose alleged malpractice they probed over the abduction of Libyan dissidents

Britain's security and intelligence agencies were last night rocked by claims that they bugged Scotland Yard detectives who were investigating the agencies’ own alleged malpractice.

A Yard spokesman yesterday confirmed that police are investigating the allegations – which stem from documents disclosed in court by MI5, MI6 and GCHQ.

If substantiated, the claims – set out in a letter to Met commissioner Sir Bernard Hogan-Howe from Cori Crider, a director of the human rights charity Reprieve – would mean that one arm of the State supposed to keep the country safe from terrorism spied on another, the Metropolitan Police.

It focuses on the case of two Libyan dissidents, Abdel Hakim Belhaj and Sami al Saadi, who were abducted from China in a joint operation by MI6 and the CIA in 2004, then sent back to Colonel Gaddafi’s Libya.

The Met launched Operation Lydd, an inquiry into their treatment, in 2012, when documents seized from the Libyan security HQ revealed that UK agencies were partly responsible. It is investigating whether British officials involved in the abduction committed crimes under English law.

A preliminary file was sent to the Crown Prosecution Service in October. But according to the letter from Ms Crider, Operation Lydd has been spied on. Behind her claims lie documents which emerged in a court hearing last month, at the Investigatory Powers Tribunal (IPT).

In these, MI5, MI6 and GCHQ made the disclosure that in cases such as those of the Libyan dissidents, they routinely bug lawyer-client conversations.

Reprieve and solicitors Leigh Day are representing Mr Belhaj, who in addition to making a criminal complaint, is trying to sue the British Government. The lawyers believe their conversations with him have been bugged, Ms Crider said yesterday, which means the agencies will also have picked up crucial details of Operation Lydd.

n her letter, she claims the documents revealed at the IPT show the agencies have apparently felt free to ‘collect communications regarding the evidence that is at the heart of Operation Lydd’. It adds: ‘If MI6 officers (or others) intercepted our contacts with police… we are concerned about the safety of potential witnesses and the risk of improper “tip-offs”.’

Ms Crider said some witnesses had come forward on terms of strict confidentiality. They would ‘fear for their lives’ if it turned out the inquiry had been bugged.

The MI5, MI6 and GCHQ (pictured) admitted in cases such as those of the dissidents Abdel Hakim Belhaj and Sami al Saadi, who were sent back to Colonel Gaddafi’s Libya, they routinely bug lawyer-client conversations

She added: ‘It seems blatantly obvious that those under investigation by the police for serious crimes should not have access to the details of that investigation. Yet that is just what we fear may have happened here.’

Lawyer-client communications have been regarded as immune to official scrutiny for centuries.