Reports say British police have started a fresh crackdown on terror suspects amid fears of an increasing flow of young Britons into Syria.
According to the Scotland Yard, a total of 24 arrests were made in 2013.
At least 16 people have already been arrested so far this year.
The detainees are accused of having links to foreign-backed militant groups inside Syria.
Reports say at least 500 British militants are operating in Syria.
European Union countries alongside Britain, one of the Western supporters of armed groups in Syria, have already expressed concerns over threat of terror attacks from extremist groups trained in Syria.
According to reports, some EU intelligence agencies have even held secret meetings with Syrian government officials about their concerns. The talks involve British, French, German and Spanish spy agencies.
The International Center for the Study of Radicalization estimated last month that nearly 2,000 militants from Western Europe are involved in the conflict in Syria.
A British defense study published last September showed that about 100,000 militants, fragmented into 1,000 groups, were operating inside Syria and carrying out atrocities against people and Syrian soldiers.
According to the study, some 10,000 militants were fighting for groups affiliated with al-Qaeda and the rest fight for different militant groups.
Syria has been gripped by a deadly crisis since March 2011.