A senior Muslim MP has claimed that the real number of British jihadists fighting in Iraq and Syria alongside Isis militants is likely to be as high as 2,000.
The UK Foreign Office has previously estimated that the number of predominantly young men travelling to the area to fight with the Islamist extremist group is closer to 500.
But Khalid Mahmood, Labour MP for Birmingham Perry Barr – a constituency in which a significant percentage of the population is Muslim – has said this is a vast underestimate of the number of British jihadists fighting in the region.
"The authorities say there are 500 British jihadists, but the likely figure is at least three to four times that," he said. "I think 2,000 is a better estimate. My experience in Birmingham is it is a huge, huge problem."
Mahmood's comments come as fears surface that authorities are unable to detect extremists leaving UK ports on their way to terror training camps.
A post on Facebook to an Islamic State-linked profile suggested that as many as 20 British jihadists are joining its forces every day, reports The Telegraph.
On Saturday it emerged that two Britons – Abu Abdullah al Habashi, 21, and Abu Dharda, 20, both from London – had died fighting in Syria. This brings the number of Britons who have died fighting up to around 30.
Dharda reportedly travelled from his home in west-London to Syria in December 2013, but was questioned by counter-terrorism police at a British airport. However, officers gave him the all-clear to travel because they were "satisfied with the explanation he gave" for the trip.
The paid are understood to have died in the Syrian border town of Kobani, which Kurdish fighters have been defending against Islamic State with the help of US airstrikes.