A new UK counterterrorism law, which received royal assent on Tuesday February 12th, means that British citizens who spend time in Syria will face arrest and imprisonment for up to 10 years upon return to their country.
Home Secretary Sajid Javed will now have the power to declare any area outside Britain a "designated area... to protect members of the public from a risk of terrorism."
The previous legislation required the authorities to prove that the returnees had already participated in terrorist activities while abroad, according to a report by AFP.
According to the new law, simply visiting these areas would constitute a crime, unless there was "reasonable excuse for entering, or remaining in, the designated area," such as humanitarian workers, armed forces, UN staff, journalists, and attending a funeral or visiting sick relatives.
Affected Britons will have a month's grace period to leave the area after the law is enacted, which is likely to be within a few months.
The government says about 900 British jihadists have travelled to Syria. Of these, 20% have been killed, 40% have returned to their homes, and an estimated 200 remain in the area.