Four men arrested by counter-terrorism police hours after flying into the country have been released under investigation.
The Sri Lankan arrived at Luton Airport on Wednesday and were arrested by police on suspicion of being members of a banned organisation the next day.
The Metropolitan Police said the men were stopped under the Terrorism Act 2000 and arrested under the Police and Criminal Evidence Act 1984.
All four men were released on Friday.
Membership of a proscribed organisation is contrary to section 11 of the Terrorism Act 2000.