- An offence introduced last month makes it a crime to travel to blacklisted region
- Currently this covers the province of Idlib, where many fighters are now trapped
- Introduced due to difficulty of collecting evidence against fighters in a war zone
British jihadists trapped in Syria face 10 years in jail upon their return to the UK under a new law that requires no evidence of them taking part in fighting.
The 'designated area' offence introduced last month makes it a crime to travel to a blacklisted region or remain there after a one-month grace period unless for a legitimate reason, such as journalism.
Currently this covers the northwestern province of Idlib, which is partly controlled by al-Qaeda-linked terrorists, but it could soon extend far wider.
A new list of designated areas will go before MPs later this year and is likely to include large parts of Syria, and parts of Libya, Afghanistan and Somalia, reported The Sunday Times.
Home Office minister Victoria Atkins recently told MPs: 'It will be an offence to remain in an area after it has been designated - even if the person has been there for some time.
Individuals will have one month to leave the area, following which they will face prosecution if they remain.'
Scores of suspected terrorists have been trapped in Idlib since 2012 after becoming sandwiched between Turkey's now-closed border and the forces of loyal to President Bashar al-Assad.
Only 40 out of 400 ISIS supporters who have come back to the UK from Syria and Iraq have so far been prosecuted because of the difficulty of collecting evidence against them in a war zone.
The British government has instead stripped some of their citizenship, including ISIS bride Shamima Begum, who joined the terrorist group after fleeing aged 15 from her school in Bethnal Green, east London.
Begum has appeared in numerous media interviews, including one in which she spoke of her boredom with hearing about Brexit from the camp where she lives in Syria.
She told The Times: 'It goes on and on without end. It's so boring now that I ask the sisters to flick on to the cartoon channel just to get away from it.'
Security Minister Ben Wallace, said: 'In order to deal with the challenges posed by terrorist safe heavens, the Government has introduced a designated area offence.
'We will not hesitate to use this as and when the opportunity arises.
'Of course for security reasons, deliberations about exactly where they will be used will remain confidential until such time as we present them to Parliament.
'Potential terrorist fighters should make no mistake that they risk up to 10 years in jail should they travel to an area once it has been designated.'