Conservatives and LibDems last night stepped up the pressure for a top-level inquiry into what they called the "shameful" leak of classified information on police counter-terrorism operations that could have put lives at risk.

David Davis, Shadow Home Secretary, wrote to Sir Gus O'Donnell, Cabinet Secretary and head of the civil service, calling on an investigation, given the "acute concernon a matter of national security" expressed by Peter Clarke, Britain's leading counter-terrorism police chief.

Mr Davis wrote: "I trust you will accept the clear public interest in proceeding with an inquiry."

Separately, Nick Clegg for the LibDems wrote to Paul Scott-Lee, chief constable of West Midlands Police, calling for an inquiry into the "terror leaks" surrounding a raid in Birmingham earlier this year.

On Tuesday, the head of the Metropolitan Police's counter-terrorism unit did not name names but surmised that "misguided individuals" might be trying to "curry favour with certain journalists or to squeeze out some short-term presentational advantage".

Mr Clarke said those who deliberately leaked sensitive information were "beneath contempt" as they compromised investigations by revealing "sources of life-saving intelligence; in the worst cases, they put lives at risk".

He highlighted leaks surrounding arrests made in Birmingham in January over an alleged plot to kidnap and behead a British Muslim soldier. The Assistant Commissioner pointed out that, even before those detained had arrived at police stations for questioning, "key details" of the investigation were leaked.

In his letter to Mr Scott-Lee, Mr Clegg called for a police inquiry into the "terror leaks" surrounding the Birmingham raid because they appeared to breach the Official Secrets Act.

The LibDems published a dossier of dozens of off-the-record briefings on terrorism issues to newspapers in the past five years, including comments attributed to "Whitehall sources".

Mr Clegg said: "There is now real evidence the government's culture of spin is undermining rather than strengthening our collective response to the terror threat. The source of the leaks referred to by Peter Clarke should be investigated urgently."

Sir Paul Lever, former chairman of the Joint Intelligence Committee, also suggested the police chief appeared to be pinning the blame on "members of the army of media advisers and spin doctors and political advisers we now have in Whitehall".

However, No 10 insisted there was no evidence that the leaks came from the government and that investigating them was a matter for others. A spokeswoman for John Reid said the Home Secretary was in agreement with Mr Clarke, adding: "National security is one of our highest priorities and anything that threatens effective operations, judicial process or counter-terrorism activity is to be condemned."

In the Commons, Tony Blair and David Cameron clashed when the Prime Minister brushed aside the Tory leader's call for a leak inquiry.

Mr Cameron asked him to guarantee the leaks had not come from either ministers or special advisers. Mr Blair replied: "As far as I am aware (they did not)."

The Tory leader said: " I'm sure you understand the damage the culture of leak and spin has done to your government. When it comes to national security this can cost lives. So will you confirm that you'll establish an independent leak inquiry, led by a senior, independent figure?"

Mr Blair insisted he would not, challenging Mr Cameron to produce evidence someone in government was responsible for the leaks.