The government potentially does not know where hundreds of Britons suspected of going to fight with Islamic State terrorists in Iraq and Syria now are.

Security Minister Ben Wallace said that around half of the estimated 850 Britons who travelled to the war zone are back in the UK, but they do not know “exactly where” many others are.

Only a fraction are thought to have been killed, and others could have crossed over into Turkey as they attempt to reach safety as the so-called ‘caliphate’ crumbles.

However, speaking to BBC Radio 4’s Today programme, Mr. Wallace insisted the authorities had not “lost track’” of the terror suspects.

“They went into a very hard part of Syria to reach into the Euphrates valley and then were dispersed from there,” he said, continuing:

“What we do know is about half have come back to the United Kingdom of the original 850-odd that went out of concern.

“About 15 per cent to 20 per cent we think have died out there either in military action, and at the moment we are seeing in dribs and drabs some of them coming into Turkey.

“Maybe some of them [are] trying to get back to us here, but there’s a significant number that at the moment it is hard to actually tie down exactly where they are.”

In October last year, a secretive government strategy named Operation Constrain was exposed, which could see suspected Islamic State fighters in Syria offered help finding jobs and privileged access to social housing.

According to official documents, as many as to 20,000 fanatics investigated by the security services could be offered the sweeteners to persuade them to reject radical Islam.

However, government minister Rory Stewart has said that the only way to deal with British Islamic State fighters in Syria is to kill them “in almost every case”.

“These are people who have essentially moved away from any kind of allegiance towards the British government,” he told BBC radio in October.

“They are absolutely dedicated, as members of the Islamic State, towards the creation of a caliphate, they believe in an extremely hateful doctrine which involves killing themselves, killing others and trying to use violence and brutality to create an eighth century, or seventh century, state.

“So I’m afraid we have to be serious about the fact these people are a serious danger to us, and unfortunately the only way of dealing with them will be, in almost every case, to kill them.”