CLEVELAND'S former CID chief Ray Mallon claims he is being followed by MI5 agents even though the long-running investigation into him collapsed without criminal charge, it emerged today.

The detective, praised by Tony Blair and dubbed Robocop for his pioneering ''zero tolerance'' policies under which Cleveland's crime rate nosedived, is still suspended from duty pending disciplinary hearings.

But today Labour MP Ashok Kumar (Middlesbrough South and Cleveland East) asked the Government to justify MI5 following Mr Mallon, if true.

''Is a cleared detective superintendent a threat to this country's national security?'' he asked, as he opened a short debate in Westminster Hall.

Dr Kumar went on to demand a public inquiry into Operation Lancet, the four-year-probe under which 61 officers were investigated for allegations ranging from supplying drugs for confessions to assaulting suspects.

The operation ended when the Crown Prosecution Service found that the evidence did not support any criminal charges. Eight officers remain suspended pending disciplinary charges.

Dr Kumar blamed Cleveland's Chief Constable Barry Shaw and other senior officers for launching the lengthy and costly investigation after believing the word of ''convicted criminals above that of hard working, respected detectives''.

He said: ''In a decision driven by petty jealousy and self-interest, the senior officers ... embarked on a witch hunt, a witch hunt to equal the best that Salem could offer.''

Dr Kumar claimed Operation Lancet had cost £7 million, levelled 400 criminal charges against 61 individual officers, taken 3,162 statements and compiled 2,444 separate police reports.

Yet, when the officers were cleared, this had not been the end of the story, and the disciplinary hearings were proceeding.

In a speech marked by vivid language, Dr Kumar accused the hierarchy at Cleveland police of engaging in four years of ''cover up and concealment'', and claimed Mr Mallon had been subjected to ''peculiar and sinister practices''.

''Can anyone now suggest that the spending of such a massive amount of public cash was the best use of police resources?'' he asked.

''People in Cleveland want a fully public inquiry into Operation Lancet, so that those who cannot speak now can have their say, so that ... petty jealousies can be exposed, so that blame can be apportioned,'' he declared.

Minister for the Police John Denham, responding to the MI5 claims, said that he could neither confirm or deny the allegation

On the question of the ongoing disciplinary charges, Mr Denham said this was an operational matter for the chief constable and it would not be right for the minister to intervene.

He went on: ''Public confidence in the police service rests on its reputation for integrity.''

Cleveland police had acted robustly by initiating investigations into the allegations against the officers.

''I share the concern of Members for the length of time to bring matters to conclusion.''

He disputed the cost of Operation Lancet, saying his figure was £3.25 million, but conceded this was still ''a substantial sum''.

Responding to the call for a public inquiry, he said ex-Home Secretary Jack Straw had announced an independent review into the conduct of Operation Lancet to identify lessons to be learnt for the future.

Read more about Operation Lancet here.

Updated: 16.15 Wednesday, July 18