Four people arrested on suspicion of being a member of a proscribed organisation have been released on police bail.
Counter Terrorism Policing officers from the Eastern Region Specialist Operation Unit (ERSOU) arrested the individuals after they arrived at London Luton Airport on Saturday, 5 and Sunday, 6 October.
The investigation is now being led by the Met's Counter Terrorism Command, supported by ERSOU.
The four people - [A] a 35-year-old woman; [B] a 39-year-old man; [C] a 35-year-old man and [D] a 41-year-old man - are all Sri Lankan nationals and were all arrested under section 11 of the Terrorism Act, for membership of a proscribed organisation.
All four were arrested under PACE legislation.
They have since been bailed to return to a south-London police station in early November, pending further enquiries.