UP to 50 detectives are working on Operation Rubicon, Strathclyde Police's inquiry into alleged phone-hacking, The Herald has been told.

A well-placed source said numbers varied from time to time but have now reached as high as 50, making the inquiry, led by Detective Superintendent John McSporran, one of the biggest of its kind undertaken in Scotland.

It rivals Operation Weeting, the probe into phone hacking being undertaken by the Metropolitan Police.

Strathclyde Police would not comment on how many are on Operation Rubicon.

But officers are believed to have begun examining the 11,000 pages of notes seized from Glenn Mulcaire, the private investigator hired by the News of the World, who was jailed for phone-hacking. It is thought that these notes contain many thousands of names.

Detectives are also scouring the 1100 names in a dossier, given to them by Tommy Sheridan’s solicitor, Aamer Anwar. The former Scottish Socialist Party leader was jailed for perjury in a case involving the News of the World.

Sheridan claims he was targeted by Steve Whittamore, a private detective used by the newspaper.

Strathclyde Police are examining allegations on phone hacking, breaches of data protection law, perjury against News International staff including Prime Minister David Cameron’s former communications director, Andy Coulson, an ex-editor at the News of the World, and police corruption.

Mr Anwar said: “My understanding is a huge amount of resources are being devoted to this,”

He believes Scottish detectives were now working with their counterparts in London but it could take many months before any conclusion.

On Tuesday, a letter emerged by Clive Goodman, the paper’s former royal editor, jailed for his involvement in the scandal. It suggested the practice was discussed at executive level meetings until it was banned by Mr Coulson.

Meanwhile, the Independent Police Complaints Commission threw out allegations against Sir Paul Stephenson, the former Metropolitan Police commissioner, and John Yates, his former assistant.

Sir Paul resigned in July after it emerged Scotland Yard had hired Neil Wallis, a former deputy editor at the News of the World, as an adviser.

Sir Paul said he had expected the ruling, but regretted resource were spent on the matter.

An independent investigation into allegations Mr Yates secured a Scotland Yard job for the daughter of Mr Wallis will continue.