UK Home Office data shows that only 54 fighters from the UK suspected of having fought in Syria and Iraq have been convicted of anoffence, 'The Sunday Telegraph' reports.
Security services estimate that since 2012, 400 British Muslims who have joined terrorist groups such as Islamic State (ISIS) and Al Qaeda have returned to the UK.
Experts on the conflict told the newspaper the number who have returned could be as high as 800 to 1,000.
The figures of returning terror suspects were disclosed by Lord Keen of Elie, a Home Office spokesperson in the House of Lords, who made public the number of prosecutions in response to a parliamentary question.
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He said the Crown Prosecution Service (CPS) was also in the process of prosecuting a further 13 cases involving 30 defendants.
The Public Prosecution Service for Northern Ireland is also dealing with one Syria-related prosecution.
Prof Anthony Glees, head of the University of Buckingham's Centre for Security and Intelligence Studies, said: "The hundreds of British citizens who have gone to Syria are highly dangerous. The fact so few are being prosecuted when they return is clearly very unsatisfactory and will be very alarming to many people.
However, some returning suspects have also received stiff sentences.
In February, a mother who took her toddler son to Syria to become an ISIS terrorist was jailed for six years.
In 2014, two British men who went to Syria to join an Al Qaeda-linked terror group were jailed for nearly 13 years.
A Home Office spokesperson said: "Everyone who returns from Syria or Iraq can expect to be subject to investigation to determine if they pose a threat and they should be in no doubt we will take the strongest possible action to protect our national security.