The Tories will urge Charles Clarke, the Home Secretary, to allow intercept evidence when the three main parties hold talks today on the Counter Terrorism Bill proposed by the Government.
Mr Clarke is prepared to look at the issue again but is unlikely to reverse his decision months ago to rule out the use of telephone taps.
Although the Metropolitan Police support the idea, it is opposed by the security and intelligence services, who believe the disadvantages would outweigh the benefits. They say terrorists are wary of using the telephone and that it would be difficult to prove in court that intercepted calls had not been tampered with.
David Davis, the shadow Home Secretary, said yesterday that a judge could collate such evidence in a way fair to both sides and it could be used in a way that "does not allow defence lawyers to go on fishing expeditions". He added: "Those are the sort of proposals we would like to see more of."
Mr Davis hoped for a "a pretty constructive outcome" to today's talks and welcomed the Government's plans to create three new offences to outlaw acts preparatory to terrorism, terrorist training and "indirect incitement" to terrorism.
Mr Clarke wants to secure all-party backing for his legislation to maintain the broad political consensus since the attacks in London. But the Tories said they would not give a "blank cheque" to ministers and there are signs that the plan to ban "indirect incitement" is running into controversy.
Mark Oaten, the Liberal Democrats' home affairs spokesman, who will attend the meeting, backed legislation covering the two other offences but said: "I will be raising some practical concerns to see how the new offence of inciting terrorist activity can be made effective."
Shami Chakrabarti, director of the human rights group Liberty, said: "What does 'indirectly inciting terrorism' mean? If it is too broad, and there is visible injustice, a new offence of that kind could actually make things a lot worse."
Sadiq Khan, the Labour MP for Tooting, warned that the proposed laws could weaken the fight against terrorism if certain sections of the community were targeted. on GMTV's Sunday programme, he said: "Will the neighbour, the family member, the person you have wrongly stopped and searched today or put under some control order or other, the next week or the week after proactively come forward and assist you the authorities in fighting terrorism and fighting crime? That is the concern."
Tomorrow Tony Blair will urge the Muslim Council of Britain to ensure mosques tighten their vetting procedures to clamp down on extremist clerics or face outside regulation.
The Government will also announce today that it is to donate £1m to the relief fund for the victims of the London bombings. It will also fast-track claims under the criminal injuries compensation scheme.