David Cameron and Nick Clegg will try to reach agreement on the Prime Minister's plans for new measures to counter the terror threat posed by Islamic State (IS) extremists, with the Liberal Democrats insisting that the changes will need careful consideration and must be based on evidence.
The Prime Minister will make a Commons statement on Monday to announce steps to close "gaps in our armoury", including new legislation to make it easier to take people's passports away to prevent them from travelling to Iraq and Syria.
The proposals come in response to the raising of the terror threat level in the UK, with experts warning that an attack was "highly likely".
A Lib Dem source said Mr Clegg and the Prime Minister were in "constant communication" on the issue and "we will consider very carefully any new proposals that are put to us".
Mr Cameron, who is meeting European leaders in Brussels where he will push for co-ordinated EU action to track jihadis, has insisted there will not be a "knee jerk response" to the threat posed by British extremists returning from the Middle East, but there were areas where more needed to be done.
"We need to do more to stop people travelling, to stop those who do go from returning, and to deal decisively with those who are already here," he said.
"This will include further steps to stop people travelling, with new legislation that will make it easier to take people's passports away."
The Lib Dem source said: "We wanted to avoid any knee jerk responses and the Prime Minister made very clear that he agrees with that."
The source said it was clear that "any new proposals would be discussed carefully, based on the evidence and with regard to the liberty of British citizens".
Speculation is mounting that the Government could bow to pressure for terrorism prevention and investigation measures (Tpims) to be beefed up. There have been calls for powers to impose "internal exile" on suspects, a key part of the old control orders regime, to be restored.
Labour leader Ed Miliband suggested the Government should "revisit" the decision to scrap control orders in favour of Tpims.
He said the Government should take action to stop young Britons being drawn to extremist ideology, with tougher measures to prevent would-be jihadis travelling to join Islamic State (IS) fighters in Iraq and Syria.
Mr Miliband also suggested a mandatory programme of deradicalisation for those involved on the fringes with IS and called for ministers to revisit the decision to scrap the control orders regime for terror suspects.
Writing in The Independent, Mr Miliband stressed the need for a "multilateral alliance" combining political, diplomatic and humanitarian action to counter the "perverted mission" of IS in the Middle East.
In the UK, he said, "we should act with clarity and determination" to tackle the threat from extremists.
"Such action must include an overhaul of the Home Office Prevent programme to equip communities with the tools to stop young people being sucked into extremist ideology," he said.
"We should also do more to prevent potential fighters from travelling to the region, and promote an effective, mandatory programme of de-radicalisation for anyone who is drawn into the fringes of extremism in Syria and Iraq."
He highlighted concerns raised by David Anderson, the independent reviewer of counter-terrorism legislation, about the effectiveness of Tpims.
Mr Miliband said: "For the most serious and high-risk cases, as the independent reviewer on terrorism has recommended, the Government should strengthen existing powers, including revisiting the case for control orders."
The threat level was raised from substantial to severe by the Joint Terrorism Analysis Centre (JTAC) due to fears about British jihadists returning from Iraq and Syria.
The change means a terrorist attack is considered "highly likely", although Home Secretary Theresa May stressed there was no specific intelligence.
"The increase in the threat level is related to developments in Syria and Iraq where terrorist groups are planning attacks against the West," Mrs May said. "Some of those plots are likely to involve foreign fighters who have travelled there from the UK and Europe to take part in those conflicts."
In Brussels, Mr Cameron will use the meeting of EU leaders to launch a fresh push for a measure which would make it easier to track the movement of potential jihadis.
The UK wants to revive a directive that would enable police and security services across the EU to share passenger records.
National leaders have signed off the arrangements - but they have stalled in the European Parliament after MEPs expressed concern about civil liberties and privacy.
In a sign of Lib Dem unease at the prospect of measures which could restrict civil liberties, former leader Lord Ashdown said politicians should not act as "cheerleaders" for the demands of the intelligence and security services.
Writing in The Observer, he said the Tories had used the decision to raise the terror threat level " to tell us how frightened we should be and why this required a range of new powers for them to exercise".
Lord Ashdown said the threat of terrorism had been faced before " effectively, without panic and without a whole new range of executive powers that could endanger our liberties".
He said: " Of course, in these circumstances, the police and the security services will lead the clamour for more powers. They are charged by us to maintain our safety.
"It is natural they should want the most powerful weapons to enable them to do so. That's their job. But it is the job of politicians to act, not as cheerleaders for those demands, but as jealous protectors of our liberties who measure any demand for their reduction against necessity, supported by evidence.
"David Cameron seemed to support this view when he said recently there should be no knee-jerk reactions. Since when, ahead of Monday's parliamentary debate, senior Tory ministers have indulged in a spasm of knee-jerking which would have made even St Vitus feel concerned.
"And Labour, frightened as always when it comes to liberty and security, capitulates to the demand. It is difficult not to conclude that there is as much domestic politics at play here as there is national security.
"I have no objection to what Nick Clegg has called specific, proportionate responses to strengthen our hand in tackling this threat. But these must be evidence based, careful of our liberties and sensitive to the need to keep moderate Islam on our side."
Lord Ashdown, who insisted that international diplomacy rather than domestic action was needed, criticised the Prime Minister's rhetoric about the struggle against Islamist extremism, claiming it would alienate moderate Muslims.
"He recently told us that this fight was about defending 'Western values'. I cannot think of any phrase, short of those used by George Bush during the Iraq war, which more damages our ability to win this battle."