Labour has accused the Government of "disarray" over new anti-terror proposals, after differences emerged within the coalition over plans to beef up controls on suspected extremists.
David Cameron yesterday told MPs police will be given powers to seize passports from UK nationals suspected of going to fight for Islamic State (IS) in Iraq or Syria.
The Prime Minister said officials were also "working up" proposals to bar British extremists from returning to this country, and signalled he wanted to toughen terrorism prevention and investigation measures (Tpims) which impose restrictions on the activities of terror suspects who have not been convicted of any crime.
However, Downing Street later admitted there was as yet no timetable for introducing legislation, and they were not certain excluding Britons from the country would be possible.
Meanwhile, the Liberal Democrats insisted they had not "definitively" signed up to bolstering Tpims by allowing suspects to be relocated.
Shadow home secretary Yvette Cooper said that the Prime Minister, who promised tough changes to the law in a press conference on Friday in which he warned that jihadis linked to IS posed "a greater threat to our security than we have seen before", had been "trying to make policy on the hoof for the sake of short-term headlines" and said his policy was now "in complete disarray".
"This chaos is a disgraceful way to develop something as important as national security policy," said Ms Cooper.
"On Friday David Cameron claimed he was about to introduce new policies, he briefed lots of measures over the weekend, and now every single one of them seems to be unravelling. If he hadn't worked it out, why on earth did he call a press conference and make big announcements?
"Over the weekend, the Government said they intended to block suspected British terrorists from returning to the UK. Yesterday they admitted they had to comply with international law and could not remove citizenship after all. But the Prime Minister still claimed to have vague plans to stop people even though no-one at all can explain what he is talking about.
"Yesterday the Prime Minister said the Government would finally respond to calls from the Labour Party and the Independent Reviewer of Terrorism, David Anderson, and would reintroduce relocation powers. However, today the Deputy Prime Minister has said his party does not support such a measure and is looking at alternative options
"Yesterday the Government said it will draw up new legislation to allow the police to confiscate passports of suspected terrorists. But the Independent Reviewer has said there is no detail on how this will work in practice.
"And there is still no timetable for any of these changes to be made, or when any legislation might be brought in."
In a series of broadcast interviews, Mr Clegg repeatedly sidestepped questions over whether the possibility of stripping suspected British jihadis of their citizenship was now effectively dead in the water, but said proposals must meet international law.
He told the BBC Radio 4 Today programme: "It's not a question of whether I will or won't let it happen.
"We are not going to do something which flouts international and domestic law. We must act within the law."
The Deputy Prime Minister insisted that the Government "can square the circle" of filling the gaps in Britain's terror laws while remaining within international obligations.
Senior coalition figures have been engaged in detailed negotiations about the package of measures over the weekend, after the UK's terrorist threat level was raised from substantial to severe.
Addressing the Commons yesterday, Mr Cameron said thousands of European citizens had gone to fight for IS and there were growing fears about the potential for them to return and wreak havoc.
"Adhering to British values is not an option or a choice," he said.
"Passports are not an automatic right. The Home Secretary already has the discretion to issue, revoke and refuse passports under the royal prerogative if there is reason to believe people are planning to take part in terrorist-related activity.
"But when police suspect a traveller at the border, they are not currently able to apply for the royal prerogative and so only have limited stop-and-search powers.
"We will introduce specific and targeted legislation to fill this gap by providing the police with a temporary power to seize a passport at the border, during which time they will be able to investigate the individual concerned.
"This power will include appropriate safeguards and oversight arrangements."
The premier said it was "abhorrent" that British citizens who pledged allegiance elsewhere were able to return to the UK and pose a threat to national security.
"We are clear in principle that what we need is a targeted discretionary power to allow us to exclude British nationals from the UK and we'll work proposals on this basis with our agencies in line with our international obligations and discuss the details on a cross-party basis," he added.
"We will introduce new powers to add to our existing terrorism prevention and investigation measures including stronger locational constraints on suspects under Tpims either through enhanced use of exclusions zones or through relocation powers."
Airlines will also be hit by tougher rules, including providing information on passenger lists, or their flights will be blocked from landing in the UK.
Downing Street said the plans for seizing passports, excluding British nationals and toughening Tpims would all require legislation.
The PM's spokesman said the changes would be brought forward "as swiftly as possible", although he declined to speculate on whether it would be this year.
He also rejected the idea that the Government was U-turning by re-introducing locational restriction, arguing that there were still significant differences between Tpims and the old control order regime.