Suspected jihadis, including teenagers, who travel to Syria will be prevented from returning to Britain for two years and only allowed to re-enter if they consent to face trial, home detention, regular police monitoring or go on a deradicalisation course.

The plan, agreed after months of internal Whitehall talks, has been cleared by government law officers and devised to minimise legal claims that the British government will be rendering citizens stateless by barring them from the UK.

David Cameron revealed the plans in a speech to the Australian parliament in Canberra. It fulfils his pledge to MPs in September to introduce new anti-terror laws after the beheading of the US journalist James Foley and the raising of the UK’s terror threat level.

The move has been agreed with the Liberal Democrats, although Lib Dem sources made clear they were unhappy that Cameron had chosen to unveil the measure in the Australian rather than British parliament and pointed out that the plan had been diluted from previous suggestions.

A detailed counter-terror bill covering the right to leave the UK and to return, as well as tighter restrictions on airlines, will be introduced this month and rushed on to the statute book by January. The bill will also give senior police officers and border police at ports on-the-spot powers to seize passports temporarily and so prevent suspected jihadis travelling abroad.

The security services say up to 500 Britons have travelled to Syria, with as many as 250 returning, and that the number of plots detected in Britain has risen markedly this year with many being hatched by radicalised young British citizens returning from Syria or Iraq. Figures from the first few months of this year show the highest proportion of travellers to Syria have been between 16 and 21.

David Cameron is to say the extremists narrative – the root cause of the terrorist threat – has to be addressed. Photograph: Suzanne Plunkett/REUTERS

At present only the home secretary, Theresa May, has the power to ban British citizens from travel by signing the royal prerogative, an executive power. Now the police will be entitled to act of their own accord: a senior police officer will need only to have reasonable suspicion that an individual is going abroad to engage in terrorism-related offences.

Passports could be seized for up to 30 days, with a magistrate’s review after 14 days. This will also apply to travellers under 18.

An individual’s passport could be seized multiple times if they sought to travel again for terrorism-related activity and they would be prevented from obtaining a replacement British passport while their existing one was held. They would also be placed on the no-fly list for the duration of the order. If the senior officer bans the same person from travelling three times the decision can be subject to a review by a magistrate.

A Liberal Democrat source said: “What is conspicuous by its absence from this package is the complete removal of passports because the prime minister jumped the gun in announcing something on that the security services did not want. They wanted managed return, and that is what will be in the bill. Apart from the civil liberty concerns no one wants people stuck on a border indefinitely.”

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The package will also include expected new powers to require airlines to provide details of passenger lists in real time or face a ban from landing in the UK. But the most controversial aspect, and the one most likely to be challenged by human rights lawyers, will be powers to prevent suspected terrorists returning from abroad for up to two years.

The home secretary, acting on the basis of “reasonable suspicion of involvement in terrorist activity”, will be able to impose a temporary exclusion order on a suspect, leading to the cancellation of their passport and the inclusion of their details on the no-fly list. The order would be served on the person’s last known home address in the UK.

The individual would only be allowed to return to Britain if, after an interview with the security services, they consent to be escorted by UK authorities and agree that they may be prosecuted, placed on a terrorism prevention and investigation measure (Tpim) or be required to adhere to strict bail-like conditions including interview with the police, regular reporting, notification of change of address and engagement in counter-extremism activities.

At present only the home secretary, Theresa May, has the power to ban British citizens from travel by signing the royal prerogative. Photograph: Luke Macgregor/Reuters

A person wishing to return to the UK would be interviewed abroad by security officials. They would retain British citizenship abroad, and so not be rendered stateless, government officials say, as they will have the option to return, albeit only on the terms of the UK government. Britain is signatory to two UN conventions on statelessness, and the former Conservative attorney general Dominic Grieve has previously said removing an individual’s passport on even a temporary basis is likely to be a legal non-starter.

The planned rules open the possibility of a suspect who refuses to return to the UK to face trial being left marooned outside the UK for an extended period, an arrangement that is unlikely to be popular if they are trapped on the European mainland.

In his speech to the Australian parliament Cameron praised prime minister Tony Abbott’s own tough set of counter-terrorism measures, but also argued the extremists’ narrative – the root cause of the terrorist threat – had to be addressed. He said:“Let’s be frank. It’s not poverty, though of course our nations are united in tackling deprivation wherever it exists. It’s not exclusion from the mainstream. Of course we have more to do, but we are both successful multicultural democracies where opportunities abound. And it’s not foreign policy.

“Now I can show you examples all over the world where British aid and British action have saved millions of Muslim lives, from Kosovo to Syria. But that is not actually the real point – in our democracies we must never give into the idea that disagreeing with a foreign policy in any way justifies terrorist outrages.

“No, the root cause of the challenge we face is the extremist narrative. So we must confront this extremism in all its forms. We must ban extremist preachers from our countries. We must root out extremism from our schools, universities and prisons.

“As we do so we must work with the overwhelming majority of Muslims who abhor the twisted narrative that has seduced some of our people. We must continue to celebrate Islam as a great world religion of peace.”He conceded “the battle for equality of opportunity for every person of every race and creed are not yet fully won, but say both Australia and the UK are places where “people can take part, have their say and achieve their dreams. Places where people feel free to say, ‘Yes, I am a Muslim, I am a Hindu, I am Christian, but I am also a Briton or an Australian too.”

The new requirements on airlines will compel carriers to use interactive electronic data systems capable of receiving instructions to offload or to screen any passenger. Civil penalties will be applied for non-compliance.

Airlines will also be required to refuse the right to board to UK citizens who are subject to a temporary exclusion order, foreign nationals reasonably suspected of terrorist activity and individuals reasonably suspected of posing a direct threat to the security of any aircraft, ship or train. Civil penalties will apply to carriers who transport to UK people to the UK whom they were refused authority to carry.

The package does not at this stage – largely due to disagreements with the Liberal Democrats about plans to reintroduce revised controls orders – include powers to direct people to be relocated within the UK. There is also no mention of plans to remove citizenship from people who have pledged allegiance to Islamic State’s self-proclaimed caliphate.