Police in the West Midlands have been given an extra five days to question three men and one woman arrested on suspicion of Syria-related terrorism offences.
They can now be detained until March 4th.
Those detained include Moazzam Begg, who is suspected of attending a terrorist training camp. He previously spent nearly three years in Guantanamo Bay detention facility before being released without charge.
They were arrested in the early hours of yesterday morning.
Campaign group CAGE says it is "outraged" by the arrest of Mozzam Begg and claim the arrest was linked to the group's pending report on Syria.
A statement reads: "This arrest forms a part of the general approach by the UK security agencies which considers any travel to Syria as suspicious.
"There has been a concerted campaign of harassment against Muslim individuals and charities who get involved in supporting the victims of the Syrian crisis.
"We do not accept involvement by Moazzam Begg in any form of terrorism. He is simply one of many individuals and charities involved in Syria being viewed with suspicion in an effort to send a message to the wider Muslim community that working in Syria is no go area for them...
"Moazzam has been very open about all of his travel and all of his objectives with regards to that travel including exposing British complicity in rendition and torture. CAGE challenges the timing of Moazzam's arrest given his travel to Syria took place in December 2012.
"CAGE is worried that the timing coincides with the planned release of our report on Syria and a major news piece that was due to be televised soon.
"We are also concerned that the Police and the security services are using the wide scope of terrorism laws, and applying them in Syria to set precedents that will make legitimate activity unlawful in future."
Moazzam Begg had written quite openly about his visits to Syria. Said visited ex prisoners & aid camps & MI5 had talked to him about trips.
"MI5 was concerned about the possibility of Britons in Syria being radicalised and returning to pose a potential threat to national security," he wrote in December 2013 on the website of his campaign group CagePrisoners.
"I told them that Britain had nothing to worry about, especially since British foreign policy, at the time, seemed in favour of the rebels. At the end of the meeting I was assured by MI5 that my proposed return to Syria to continue my work would not be hindered, and it wasn't."
Moazzem Begg writing about trips to Syria said last yr passport confiscated as police said previous trips constituted terrorism involvement.
He adds that on returning from a trip to South Africa in December he was "met upon arrival at Heathrow by officials who served me with a notice to seize my passport under the 'Royal Prerogative' stating that it was assessed my previous visits to Syria had constituted involvement in terrorism."