Jacqui Smith accused David Cameron and his Shadow Home Secretary last night of behaving in a manner unfit for high office as the Damian Green affair threatened to overshadow today’s State Opening of Parliament.

The Home Secretary told Dominic Grieve that he had made “mischievous, perverse, inaccurate and unfounded” allegations as relations between the two front benches sank to a new low.

There were threats that today’s Queen’s Speech debate could be disrupted by Conservative protests.

Tory and Liberal Democrat MPs are insisting that Michael Martin, the Speaker, agree to their demand for an emergency debate after he delivers a statement defending the action of the Commons authorities in allowing the police to raid Mr Green’s office.

They want the debate before proceedings on the Government’s new programme or, failing that, tomorrow. Either way, senior figures are certain to protest about Mr Martin’s decisions after his statement.

If the debate were to take place today, Mr Brown’s appearance on one of the most important days of the parliamentary year would be delayed for several hours.

Ms Smith went on the offensive last night with an outspoken attack on Mr Grieve and Mr Cameron in which she stated that until after the arrest of Mr Green she did not know that he or any other MP was being investigated or was to be arrested.

In a letter to Mr Grieve she said his claim, that she must have known an MP was involved, ran wilfully and directly counter to statements by herself, the Civil Service and the police. Rather than seeking to dismiss the offence that the police were investigating he would do better “to show respect for the law and the duty of parliamentarians to uphold the law”, she said.

Ms Smith added that for Mr Grieve and Mr Cameron to assert that the systematic leaking of government material was not serious as it did not relate to national security was “wholly irresponsible and entirely unfit for those who seek to hold high office”.

The Times has also learnt that in addition to working in ministerial private offices, Christopher Galley, the official at the centre of the leak inquiry, was also employed in another sensitive part of the department. He worked for some time in the office of Paul Maltby, who is head of the Home Office strategic policy team.

The team is based on the third floor of the department in Marsham Street and its aim is to help the Home Office to meet its key objectives by tackling strategic issues and promoting innovation in developing policies.

Mr Galley has stood as a Conservative candidate in a council election but he was not at a grade where he would have had to inform officials or his line manager of his political affiliation, according to Home Office sources. Even if he had, that would not have debarred him from employment.

The Commons Library also cited the precedent of Lord Cochrane, who was arrested in 1815 while sitting on the government front bench in the Chamber, having escaped from prison.

Sir Gus O’Donnell, head of the Civil Service and Cabinet Secretary, appeared to stray into the controversy last night. At an awards event he said: “All civil servants serve the Government of the day. We are politically impartial and our actions are governed by the Civil Service Code.

“Political impartiality means we must serve the Government, whatever its political persuasion, to the best of our ability, no matter what are own political beliefs.

“To quote from the code, this means acting ‘in a way which deserves and retains the confidence of Ministers, while at the same time ensuring that you will be able to establish the same relationship with those whom you may be required to serve in some future government’.”

Times Recommends

• Margot Fonteyn: In her footsteps
• Forget beautiful people, let's have wonky Brits
• Fundamentalist brew: faith and power