HOME Secretary Jack Straw is to be asked to investigate claims that MI5 was used to spy on suspended senior detective Ray Mallon.

Yesterday, Middlesbrough South MP Ashok Kumar said he was "deeply concerned" and would be raising the allegations with Mr Straw.

It is claimed that on September 26, Detective Superintendent Mallon, vice-chairman of West Hartlepool Rugby Club, was followed by two cars as he drove to the Fitness First gym in Hartlepool, for a meeting with club coach John Stabler.

Earlier in the day, Jayne Thwaites, a police clerk with whom Mr Mallon had worked when he was based in Hartlepool, believes she was followed from her home as she made her way to the same gym.

The registration number of one of the cars - a black Honda Accord - was reported to police and has been traced to a Government agency, widely believed to be MI5.

The National Superintendents' Association is so concerned, it has held talks at the Home Office to brief Her Majesty's Inspector of Police about the surveillance.

Mr Mallon has been suspended under the controversial Operation Lancet inquiry into Cleveland Police for almost three years, but in June was cleared of any criminal conduct.

Miss Thwaites is a member of staff with Cleveland Police at Hartlepool. She has never been accused of any wrongdoing but is currently off sick due to stress.

Yesterday, Dr Kumar said: "I am deeply concerned at the use of Government agents in this way and will be writing to Jack Straw about this issue."

The detective's solicitor, Mike Hymanson, said: "We believe our client has been followed by a Government agency.

"We will be making formal complaints to the appropriate authorities."

Miss Thwaites has submitted a formal complaint against the Chief Constable.

Cleveland Police yesterday declined to comment.