Controversial new powers to cancel the passports of UK nationals who travel abroad to fight for the Islamic State (IS) terror group are to be included in a counter-terrorism Bill to be tabled in Parliament this month, David Cameron has said.
The legislation will block individuals from returning from Syria and Iraq to the UK for at least two years unless they comply with strict measures, which could include being escorted back to Britain and then facing prosecution, bail-style reporting conditions, deradicalisation courses or being subjected to Terrorism Prevention and Investigation Measure orders.
Border guards and airport police are to be given new powers to seize passports from individuals they suspect of planning to travel abroad for terrorism. The power will be extended to under-18s in response to fears of indoctrinated British teenagers going to the Middle East to volunteer for terror gangs.
During the first few months of this year, the highest proportion of Britons travelling to Syria and Iraq to fight were aged between 16 and 21.
Airlines will be ordered to comply with a "no-fly list" of individuals barred from travel to the UK because of suspected involvement in terrorist activities and to use interactive electronic data systems capable of receiving instructions to offload or to screen any passenger. Any airlines which bring banned individuals into the country could face civil penalties, including the removal of the right to land in the UK.
Cameron announced the proposals in a speech to the Australian Parliament in Canberra, with the aim of making them law by the end of January.
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The plans have been agreed with the Liberal Democrat side of the coalition Government following intensive negotiations after they were first outlined by Mr Cameron to the House of Commons in September in response to concerns that more than 500 UK citizens had been recruited by IS - including the notorious "Jihadi John", who is believed to have been responsible for the murders of beheaded aid workers Alan Henning and David Haines.
Notably absent from the package are measures to beef up Tpims to allow the state to dictate where in the UK individuals subject to an order can live, which raised Lib Dem hackles when floated by the PM.
Mr Cameron's proposals are likely to spark legal wrangles, with opponents expected to argue that the cancellation of passports of Britons fighting overseas would render them stateless, in contravention of international law. Former attorney general Dominic Grieve warned in September that "even taking such powers on a temporary basis is likely to be a non-starter".
But Downing Street sources indicated that the measures had been given the green light by Mr Grieve's successor Jeremy Wright. They pointed out that individuals losing their passports would retain their UK citizenship and would be permitted to return to Britain, but only if they complied with stringent conditions.
Any attempt to sneak back into the UK clandestinely after passport cancellation would be punishable by up to five years in prison.
Home Secretary Theresa May already has the power under royal prerogative to approve the seizure of passports of Britons suspected of travelling abroad for terrorist purposes, and it is thought to have been used around 24 times in the past year.
But the new measures would allow Border Force officers or police at airports and ports in the UK to use their own initiative - subject to approval from a senior officer - when they have "reasonable suspicions". Passports could be temporarily withdrawn for 30 days, with a magistrate's review after a fortnight, and individuals who try again to leave the country could have their passport withdrawn repeatedly and find themselves placed on no-fly lists.
Downing Street said the package would "significantly strengthen our armoury" in tackling the problem of foreign fighters, giving Britain the toughest system in the world after the US.
At a press conference with Mr Abbott following his speech, Cameron was asked whether the new measures would leave British militants stranded stateless in countries like Turkey.
Cameron replied: "Successive governments have come to the view - and I agree with that view - that when you are facing an existential challenge and a challenge as great as the one we face with these Islamist extremists, we need additional powers as well as simply the criminal law.
"That's why we have these powers to take away someone's passport before they travel, to ban someone from travelling. That's why we have added this additional power to temporarily exclude someone from coming back into the UK.
"We believe we need an additional set of powers in order to keep the country safe over and above what the criminal law allows, and I think it is very sensible that we do that.
"We obviously do that after debate and listen very carefully to what the police and security services advise us. We think about the civil liberties implications and we think about the effects on other countries.
"At the end of the day, I make the choices based on what I think is necessary to keep the British public safe, and I think this new power is important in this regard."
Addressing the Australian Parliament during a visit ahead of the G20 summit in Brisbane, Cameron also renewed his call for internet companies to take down extremist material from the web, saying: "This is their social responsibility. And we expect them to live up to it."
Cameron said: "We have to deal with the threat of foreign fighters planning attacks against our people. We will shortly be introducing our own new Counter-Terrorism Bill in the UK.
"New powers for police at ports to seize passports, to stop suspects travelling and to stop British nationals returning to the UK unless they do so on our terms; new rules to prevent airlines that don't comply with our no-fly lists or security screening measures from landing in the UK."
Watched by his Australian aunt Caroline in the gallery, Cameron also spoke out about the dangers of trade protectionism and - in comments seen as a swipe at China and Russia - warned against the idea that capitalist economics can be combined with political authoritarianism.
Cameron said there was an "incipient creeping threat to our values" from "those who say that we will be outcompeted and outgunned by countries that believe there is a short cut to success, a new model of authoritarian capitalism that is unencumbered by the values and restrictions we impose on ourselves - in particular, an approach that is free from the accountability of real democracy and the rule of law".
He added: "I say we should have the confidence to reject this view and stay true to our values. These attributes - our rule of law, our democracy, our free press - these aren't weaknesses, they are our greatest strength.
"We need to resist the idea that says that nations can enrich their citizens while forever bypassing the building blocks of democracy."
The PM received a standing ovation from Australian MPs, and he won laughter as he attempted an Australian accent to conclude an anecdote with the single word: "Strewth!"
The international threat from terrorism will be high on the agenda, alongside economic growth, trade and infrastructure development, at this weekend's summit of the world's 20 leading economies in Brisbane.
But the gathering is also likely to be dominated by tensions over Ukraine and tax avoidance.
Cameron has vowed to confront President Vladimir Putin over Russia's interference in Ukraine, warning him not to plunge the world into a new Cold War.
He is also expected to wade into the row over allegations that European Commission president Jean-Claude Juncker encouraged tax avoidance as prime minister and finance minister of Luxembourg.
Lord Carlile, a former inspector of terrorism legislation for the Government, said he believed the proposals being set out by the coalition would be in line with international law.
The Liberal Democrat peer also predicted that relocation powers, similar but not as extensive as in the old control order regime, would feature in the legislation.
"I expect to see that in the detail, and indeed my understanding was that was part of the deal that had been agreed," he told BBC Radio 4's Today programme.
"I would expect them to contain a measure to move people around the country, subject to of course what one would expect, which is a proper standard of proof, and possibly subject to restrictions as to how far they would be moved.
"I don't think for example it would be permissible to move someone from Land's End to John O'Groats.
"But I hope and expect it will be permissible to move them well out of the area where they have been carrying out what is in fact illegal activity."
Lord Carlile said the problem was that radicalised individuals tended to "congregate together and talk about their intentions". Moving them somewhere "comfortable and reasonably pleasant but not where they were" gave them a proper chance to change their behaviour away from radicalising influences.