A 24-year-old man has been arrested at Heathrow Airport on suspicion of committing terrorism offences.
The man was arrested by officers from the Metropolitan Police's Counter Terrorism Command after arriving on a flight from Bahrain. He was taken to a south London police station where he is being questioned over alleged terrorist activity.
A police spokesman said: "Officers from the MPS (Metropolitan Police Service) Counter Terrorism Command today, Monday November 12, arrested a 24-year-old man on suspicion of the commission, preparation or instigation of acts of terrorism under the Terrorism Act 2000.
"He was arrested at 8.45am after arriving on a flight from Bahrain to Heathrow Airport. The man was arrested after initially being stopped by immigration officials at 8am."
He added: "Today's arrest forms part of an investigation into travel to Syria in support of alleged terrorist activity."
Another man, Shajul Islam, 26, is facing trial over allegations that he was involved in the same plot. The trainee NHS doctor is charged with keeping John Cantlie and a Dutch journalist captive.
Islam, who studied at St Bartholomew's and a University of London hospital, is accused of being part of an extremist group that held Mr Cantlie, who worked for various newspapers including the Sunday Times, and Jeroen Oerlemans for around a week in the war-torn state.
Islam, from Stratford, east London, was arrested at Heathrow Airport last month as he arrived back in the UK with his wife and one-year-old daughter on a flight from Egypt. He is accused of being a doctor for the jihadi group that kidnapped the journalists and held them at a camp in Syria.
It is alleged that Islam, with others, unlawfully and injuriously imprisoned Mr Cantlie and Mr Oerlemans against their will, between July 17 and 26.
Islam is due to appear at the Old Bailey on April 12 for a plea and case management hearing, and a six-week trial is set to begin on June 5.