he senior policeman leading the investigation into an alleged plot to behead a Muslim British soldier believes the inquiry has been "hijacked" by the Government.

Assistant Chief Constable David Shaw was "seething" when he discovered Whitehall officials leaked sensitive details of Operation Gamble to the media in an apparent attempt to divert attention from the problems engulfing Tony Blair.

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And he is said to be increasingly frustrated that the anonymous briefings may be impeding his officers' efforts to gather evidence.

A source close to Mr Shaw said: "He is angry that while he had played a straight bat there are others in Government departments who, without asking him, briefed the media about his inquiry."

Last Wednesday morning, only a few hours after the dawn arrests of nine men in Birmingham, Mr Shaw watched despairingly as details of the operation he hoped would remain secret flashed up on TV.

The source said: "He said through gritted teeth, "I haven't said any of those things - it has all come from London."

At one point, to the bewilderment of senior officers, details of the operation were being broadcast while one of the suspects had still to be found.

Mr Shaw never intended for the public to know, at least not yet, the existence of the alleged beheading plot, fearing the huge publicity would only further inflame Birmingham's Muslim communities at a time when he needs their assistance.

Following the leaks, senior officers were sent to try to pacify community leaders and explain that the police were not to blame.

Mr Shaw, a married father of two, is a highly espected figure among the city's ethnic minorities and is understood to be dismayed at the rancour in the Muslim community that the interference from Whitehall has produced.

The source said: "He feels the inquiry has been hijacked by those who don't have to live - as he does - with the direct consequences of what they say publicly.

"To my knowledge, he hasn't speculated as to what motivated these people to brief the media but it's really rather obvious that there are various agendas at work here."

Mr Shaw had released only scant information about the arrests, not operational details.

But the unofficial release of lurid detail about an alleged beheading plot - and an accompanying account of how two soldiers were used as "live bait" to try to flush out the suspects - dramatically raised the interest in the story.

Conveniently for the Government, it replaced the prisons crisis as the story of the week - and took the sting out of the cash-for-honours row that saw Tony Blair questioned by police for a second time.

Mr Shaw felt it necessary to spell out his discomfort in a news conference on Friday.

Referring to Birmingham, he said: "I am acutely aware that members of the community are confused and bewildered by what is being said by the media."

The Home Office said: "We have only released factual statements on the matter and the Secretary of State and the Attorney General have reminded media not to do anything that would prejudice the operation."