The Scotland Yard unit which deals with some of the force’s most sensitive police inquiries has been “corrupted” by a firm of private investigators, leaked documents seen by The Telegraph reveal.

The company – RISC Management Ltd – was run by retired detectives who are thought to have targeted former police colleagues to secure information about the progress of sensitive Metropolitan Police inquiries. Internal Scotland Yard documents described them as operating like “an organised crime network”.

Scotland Yard set up its own anti-corruption investigation into the relationship between RISC Management Ltd and officers working in SCD6, the economic and specialist crime division of the force.

SCD6 has investigated some of the country’s most high-profile and sensitive criminal cases including the “cash for honours” probe into whether Tony Blair’s government had offered peerages to big donors and the MPs’ expenses scandal.

Officer given a 'dirty' mobile phone – intelligence

Leaked intelligence reports seen by this newspaper reveal that the anti-corruption probe found that more than 300 phone calls were made between Met police officers and RISC Management Ltd investigators over a 12-month period.

In one instance a police officer was given a “dirty” mobile phone by RISC Management so he could secretly report back what he found, the report states.