Gordon Brown has said he wants to strengthen anti-terror laws when he becomes prime minister this month.
Intercept evidence rules could change under a Brown premiership
He wants new powers for police and a fresh look at whether material from telephone tapping can be used in court.
The chancellor also wants to revive proposals to increase the time terror suspects can be held without charge from 28 to 90 days.
But he accepts any new powers should include more parliamentary and judicial scrutiny to protect civil liberties.
In a speech to Labour activists, Mr Brown said he would give the courts and Parliament "greater oversight" over his proposed counter-terror measures.
He is also reported to be intending to ask the cross-party Privy Council to review the case for allowing intercept evidence in court.
The move has until now been rejected by the government amid opposition from the security services.
Mr Brown is said to believe there could be a case for allowing it if a way could be found to protect intelligence sources.
Judges might also be allowed to take account of links to terrorism as an aggravating factor in sentencing.
And police could be given new powers to continue questioning suspects after they have been charged.
But it is the proposal to extend detention without charge that is likely to prove the most controversial.
Liberal Democrat justice spokesman Simon Hughes said Mr Brown would have a "fight on his hands" if he tried to get it through Parliament again.
And he warned: "Gordon Brown must start seeking cross-party support, because if he doesn't do that, there'll be rows and parliamentary defeats in his early days for the new prime minister."
Tony Blair's attempt to introduce 90-day detention without charge in 2005 was opposed by Tories, Liberal Democrats and some Labour backbenchers.
And Conservative sources say there is no new evidence to suggest that police need more than 28 days.
But Constitutional affairs minister Harriet Harman, one of six Labour MPs vying to be Mr Brown's deputy, said she thought MPs would back new laws - including 90 day detention - if Mr Brown could prove they were needed.
"I don't think there will be a huge problem if there is a proper debate about it - if evidence is brought forward about why current powers are inadequate and what the safeguards will be," she told BBC One's Sunday AM.
In a speech on Saturday, Mr Brown said stronger measures would have to be put in place to give the authorities the power to intervene at earlier stages of an investigation.
He said: "That's why I support, for terrorists suspects, post-questioning interviewing.
"That's why we will need to strengthen the policing resources available. But at every stage I would say this.
"Because we are a country that believes in civil liberties of the individual, every time you have to strengthen the security measures that are necessary to protect our country, you also have to strengthen the accountability to parliament and the independent oversight of what police and other authorities are doing."
Shadow Home Secretary David Davis, for the Conservatives, criticised the timing of Mr Brown's announcement.
He said: "It is extraordinary that the chancellor has chosen to publicise these proposals five days before the home secretary announces his counter-terrorism plans in Parliament.
"It does not auger well for cross-party attempts to build a consensus for counter-terrorism measures, which the whole country needs to get behind."
Shami Chakrabati, director of pressure group Liberty, welcomed the phone intercept proposals but said Mr Brown was making "a grave mistake" in proposing to extend questioning without charge beyond 28 days.
"Twenty-eight days is already the longest period to hold a person without charge in the free world. If you go beyond 28 days it is internment," she told BBC News.