LONDON — The British police said on Tuesday that they had arrested Moazzam Begg, a former detainee at the American prison at Guantánamo Bay, Cuba, along with three other people on suspicion of terrorism offenses related to the war in Syria, where, intelligence officials say, hundreds of British militants have been drawn to the fight against President Bashar al-Assad.

Mr. Begg, 45, was one of the last Britons held at the naval base in Cuba before his release and return home in early 2005. At the time, lawyers said he and a fellow detainee, Feroz Abbasi, had been held in solitary confinement for nearly two years. Mr. Begg was detained in Pakistan in 2002 and had lived in Afghanistan the previous year, when the United States-led war against the Taliban began.

The West Midlands police in Birmingham said a 44-year-old woman and her 20-year-old son were also detained, along with a 36-year-old man. The three were not identified.

Identifying Mr. Begg does not imply any guilt, a police statement confirming his arrest said. Counterterrorism police officers were said to be searching the detainees’ homes and to have confiscated vehicles and electronic equipment.