Former Guantanamo Bay detainee Moazzam Begg is one of four people arrested on suspicion of Syria-related terrorism offences today.
Begg, 45, was arrested by officers from West Midlands Police today as they carried out a series of early morning raids across Birmingham.
The British citizen has previously been held in Guantanamo by the US before being released without charge.
In recent years he has campaigned for those he claims are unfairly targeted by the war on terror and is director of the human rights group Cageprisoners.
He was arrested today on suspicion of attending a terrorist training camp and facilitating terrorism overseas.
Begg was detained at Guantanamo Bay in February 2003 before being released by former US President George Bush in January 2005.
A 36-year-old man, from the Shirley area of Birmingham, and a 44-year-old woman and her 20-year-old son, both from the city’s Sparkhill area, were also arrested on suspicion of facilitating terrorism overseas.
A West Midlands Police spokeswoman said: 'We can confirm that Moazzam Begg was arrested this morning.
'We are confirming this name as a result of the anticipated high public interest to accredited media.'
She added naming Begg does 'not imply any guilt'.
All four suspects were being held at a police station in the West Midlands and their three home addresses are being searched by officers from the West Midlands Counter Terrorism Unit.
The offences are all Syria-related, the spokeswoman added.
Officers said they were now in the process of removing vehicles and electronic equipment for forensic analysis.
Detective Superintendent Shaun Edwards, head of investigations for the regional counter terrorism unit, said: 'All four arrests are connected.
'They were pre-planned and intelligence-led. There was no immediate risk to public safety.
'We continue to urge anyone planning to travel to Syria to read the advice issued by the Foreign Office.'
Originally from Birmingham, Begg moved to Afghanistan with his family in 2001 before taking them to Pakistan in 2002 when the war began.
He was detained in Islamabad, Pakistan, as an 'enemy combatant' in January 2002 and was taken to the Bagram internment centre for about a year before being transferred to Guantanamo.
The British citizen was released along with three others in January 2005 and was allowed to return to the UK where he was arrested by the police before being released without charge.
Begg, now a director of campaign group Cage, has always maintained that he was only involved in charity business and that he has never been involved in any kind of terrorist activity.
The latest arrests today come after it was revealed about 400 British-based extremists have gone to Syria over the last two years - and just over half have returned to the UK.
In recent weeks, ministers have been told that about 250 Britons who went to train and fight in war-torn Syria are now back in the UK - with the conflict described by one top domestic security official as a 'magnet' for jihadi activity.
In January alone, there were 16 people detained on suspicion of terror offences relating to Syria in comparison to 24 arrests for the whole of last year.
At the time, a senior Whitehall source said the Syrian threat was 'serious' and presented 'real challenges for intelligence agencies'.
The Birmingham arrests follow reports of what is thought to be the first instance of a British-based jihadist staging a suicide attack on a Syrian government prison in the country.
Abdul Waheed Majeed, 41, is suspected of being responsible for driving a lorry into a jail in Aleppo and detonating a bomb earlier this month.
He is among an estimated 20 Britons who have been killed in the fighting in the war-torn state.
In January, photographs were published of two British brothers from north London believed to have died in battle in the war-torn country in September who were reportedly hailed as 'martyrs' and 'young British lions' by Syrian rebels.
A patchwork of rebel groups, counting extremist jihadist fighters among their ranks, have been engaged in an intractable and bloody conflict against the government of Bashar al-Assad, which has claimed at least 100,000 lives, since 2011.
Meanwhile in the UK, two women appeared in court last month accused of trying to send £16,500 to fund alleged Islamic terrorists fighting in Syria.
Londoners Nabal Masaad, 26, and Amal El-Wahabi, 27, are due to appear at the Old Bailey in May.
Security officials and senior politicians have been warning for months of the potential surge in radicalised foreign fighters returning to the UK from war-torn Syria.
MI5 director-general Andrew Parker told MPs last year that the civil war in Syria has been a magnet for hundreds of British nationals looking for the opportunity for 'jihadi' activity, many of whom have come into contact with al Qaida-supporting groups before returning to the UK.
Home Office minister James Brokenshire recently said the issue now formed a significant and growing area of focus for the British security services and warned concerns over terror-related and jihadi activity linked to Syria were 'likely to be with us for the foreseeable future'.
Via Caz Booth