Gavin Williamson signalled he was prepared to hunt down and use air strikes against the remaining 270 UK passport holders who have travelled to Syria and Iraq.

The new Defence Secretary today was accused of dreaming up a policy which belongs in a Netflix series after he suggested all British terrorists who fight for ISIS should be 'eliminated'.

Gavin Williamson told the Daily Mail Britons who have fought for terror group should never be allowed to come back to this country.

And he said those who were intent on bringing 'destruction, death and bloodshed' onto the streets of the UK were being 'hunted down' and that threat 'eliminated'.

But his comments have sparked a row after the former director of public prosecutions Lord MacDonald branded the remarks 'juvenile'.

He said: 'It simply will not be lawful in all circumstances to kill jihadis, as the secretary of state seems to be suggesting.

'A policy which says we will simply kill every individual who has travelled to Syria or to Iraq, even if they are surrendering, even if they have laid down their weapons, is really a policy that belongs in a Netflix series more seriously than it belongs in the range of policies that should be being applied by the UK government.

'We can't simply say that everyone who has gone to Iraq will now be hunted down and killed.

'That's a juvenile response. It's not a serious, grown-up policy response for a senior British Government minister.'

Liberal Democrat defence spokesman Lord Menzies Campbell said the comments 'are ill-considered and appear to endorse a clear breach of humanitarian law'.

Lord MacDonald, pictured in the House of Lords last month, branded Gavin Williamson's remarks 'juvenile'.

He said: 'In present circumstances it is not difficult to see that any member of the military that followed his advice could be subjected to court martial and prosecution.

'The gung-ho opinions that he has expressed undermine the credibility of British armed forces in general and his office in particular.'

But Downing Street today backed Mr Williamson's comments and said Britons who fight for ISIS are 'legitimate targets' for military strikes.

The Prime Minister's official spokesman said: 'The Government position on this has been made clear a number of times in recent months, which is that if you travel to Iraq and Syria and if you are fighting with our enemies there, then you make yourself a legitimate target.'

He added: 'There are existing powers in relation to foreign fighters who seek to return to the UK.

'They include expulsion orders that allow the UK to cancel an individual's passport.

'In instances where people do return to the UK, we are clear they should face the consequences of their actions, which include investigation by police and possible prosecution.'

In an interview with the Daily Mail, Mr Williamson signalled he was prepared to hunt down and use air strikes against the remaining 270 UK passport holders who have travelled to Syria and Iraq.

He said: 'Quite simply, my view is a dead terrorist can't cause any harm to Britain.'

He added: 'I do not believe that any terrorist, whether they come from this country or any other, should ever be allowed back into this country.

'We should do everything we can do to destroy and eliminate that threat.'

Labour MP and former paratrooper Dan Jarvis said his comments were 'morally, legally and practically wrong'

Mr Williamson's comments are the starkest yet on the issue of whether British jihadists should be allowed to return home to the UK.

In October, Britain's terror watchdog, Max Hill QC, sparked a row by suggesting that some young people who had travelled to Syria and Iraq should be allowed to come home and re-join society.

He said that it was not worth losing a generation of young people who 'naively' went to join Islamic State.

But Mr Williamson's remarks appear to be an emphatic rejection of that argument.

More than 800 UK citizens are thought to have gone to fight for Islamic State in Iraq and Syria. Around half of them have already returned, and around 130 have been killed, leaving an estimated 270 left.

London-born Lucas Kinney (left) converted from Catholicism and become an Al Qaida fighter in Syria. Jihadi John (right) was also originally from the UK

Earlier this year, the Mail revealed that RAF pilots had been secretly assassinating British jihadists in Syria and Iraq, using drones and fighter jets to work through a 'kill list' of targets - particularly those plotting attacks back in the UK.

In his interview, Mr Williamson condmened British citizens who had gone abroad to join terrorist organisations 'that hate everything that Britain stands for, hate our values, hate that Britain is as a beacon to the world of democracy and tolerance.'

He said it was right that Britain's forces were trying to tackle that threat - to stop those people from returning home to launch attacks here.

'Our forces are right across the globe degrading and destroying that threat, making sure that these people who want to bring destruction, death, bloodshed onto our streets aren't able to come back,' he said.

'That is as important part of the jigsaw as what we actually do on the streets in Britain.

New figures reveal how Britain has dramatically increased its drone strikes in Syria (Reaper drone pictured)

'Every day we have got British service personnel making a difference to make sure some of those people that want to cause that harm are never able to come back to this country. That is something I am incredibly proud of.

'I do not believe that any terrorist, whether they come from this country or any other, should ever be allowed back into this country.

'We should do everything we can do to destroy and eliminate that threat.'

Defence sources made clear that UK terrorists in Iraq and Syria would either be taken out in airstrikes by warplanes or drones operated from RAF Waddington in Lincolnshire.

Mr Williamson said: 'Quite simply my view is a dead terrorist can't cause any harm to Britain.'

The lawyer who wants jihadis spared The terror watchdog was accused of a 'reckless disregard' for society earlier this year after he called for 'naïve' teenage jihadis to be spared prosecution. Max Hill, the independent reviewer of anti-terror laws, said militants returning from the Islamic State war zone should instead be given space to reintegrate. The top lawyer warned against losing a generation of young men and women brainwashed by online propaganda. He said those who returned in a 'state of utter disillusionment' could be 'diverted' from the criminal justice system. Mr Hill, who took the role in February, said travelling to Syria should not always mean prosecution. He said: 'We should be looking towards reintegration and moving away from any notion that we are going to lose a generation due to this travel.' But a top RAF commander said last month that the idea that British jihadis who travelled to the IS war zone did not know what they were doing was 'fanciful'. Air Commodore Johnny Stringer said UK jihadis had made themselves 'valid' targets by going to the war zone. Advertisement

The Defence Secretary also pledged that those British fighters who had 'splintered' and fled to other countries would also be found and prevented from returning to the UK.

It is understood they will have their passports taken off them if they try to cross over international borders.

'We have got to make sure that as (they) splinter and as they disperse across Iraq and Syria and other areas, we continue to hunt them down,' he said.

'Make sure there is no safe space for them, that they can't go to other countries preaching their hate, preaching their cult of death.'

The former chief whip, who was given the Cabinet job only last month, added: 'Our job in terms of eliminating that will not stop this year, will not stop next year, it is something we have got to continue to pursue.

'That is about keeping Britain safe just as much as making sure we have the right response here in Britain.'

Mr Williamson said the Armed Forces stands ready constantly to do whatever is needed to keep Britain safe from terror attacks

His comments came as new figures reveal how Britain has dramatically increased its drone strikes in Syria, where the remaining UK foreign fighters are believed to be plotting attacks on British soil.

Figures disclosed by the Ministry of Defence show there was one Reaper strike in 2015, compared to 24 strikes in 2016, and 31 strikes in 2017.

In Iraq there have been a total of 352 Reaper strikes since the war began in 2014, 663 strikes by Tornados and 402 strikes by Typhoons.

Mr Williamson said the Armed Forces stands ready constantly to do whatever is needed to keep Britain safe from terror attacks.

He added: 'But let's not underestimate the role that they are playing actually on foreign fields. Yes the threat manifests itself on the streets of Great Britain.

'But actually so much of what is done to activate it is done in places, whether it be Libya, whether it be Iraq, whether it be Syria.

'And we have a duty, and this is what we are doing right across the globe, degrading and destroying that threat.'

Coalition airstrikes have killed about 45,000 IS fighters up until August last year.

In September a top commander said secret strikes by RAF warplanes against jihadists in Iraq and Syria had stopped a series of home-grown terror attacks.

The head of MI5, Andrew Parker, has said the terror threat facing the UK was at the 'highest tempo' of his 34-year career

Air Commodore Johnny Stringer admitted British citizens had also been killed in the missions against Islamic State strongholds.

The extremist group has a special unit dedicated to mounting atrocities in the UK and Europe.

The head of MI5, Andrew Parker, has said the terror threat facing the UK was at the 'highest tempo' of his 34-year career.

On Tuesday the spy chief told the Cabinet that British spies have foiled nine terror attacks in the UK in the past 12 months.

The thwarted attacks included alleged plans to create carnage at tourist attractions, government buildings, pop concerts and carry out knife and vehicle rampages.