The controversial Operation Lancet inquiry into alleged corruption among Britain's most successful crime-fighting squad in believed to have ended with all 393 criminal allegations being thrown out.

There are renewed calls for a public inquiry into the three-year probe which is estimated to have cost the taxpayer more than £6m and tied up dozens of frontline officers.

Detective Superintendent Ray Mallon - dubbed Robocop for his highly successful Zero Tolerance policing strategy -was the most famous casualty of Lancet.

He was suspended from duty along with seven of his detectives from Middlesbrough CID. A further 53 officers from Cleveland Police were also investigated.

Yesterday, high-level sources revealed the CPS had informed Cleveland Police that there was "no evidence" to support any criminal proceedings.

An official announcement in expected within days but the source said Cleveland Police is now trying to persuade the CPS to change "no evidence"to "insufficient evidence".

Lancet began as an internal probe within Middlesbrough CID, but mushroomed into the biggest corruption inquiry ever handled by the Police Complaints Authority.

In his most recent report into the force, Her Majesty's Inspectorate of Constabulary, Dan Crompton, warned: "There is a need for such inquiries to remain focused."

Communications manager Joanne Malone recently quit the force in disgust at an alleged "dirty tricks" campaign against Mr Mallon.

She alleged that Chief Constable Barry Shaw was implicated in the leaking of a confidential Treasury Counsel document. Her complaint is being invesigated by South Yorkshire Police