Two former Guantanamo Bay detainees from the West Midlands were stopped under anti-terror laws at an airport, according to a human rights group.
The 'Tipton Three' were released without charge in 2004
Reprieve said two actors, who play the so-called Tipton Three in a new film, were also held at London Luton Airport.
They were returning from the Berlin Film festival after winning an award.
Police said no arrests were made but four out of six people were "stopped" for an hour under the counter terrorism act, as they tried to enter the UK.
The Winterbottom-directed drama The Road to Guantanamo won a Silver Bear award at the Berlin Film Festival.
It is about the lives of Ruhal Ahmed, Asif Iqbal and Shafiq Rasul, from Tipton, who were detained at the US military base in Cuba for more than two years before they were released without charge in March 2004.
Reprieve, acting on behalf of one of the actors, said Mr Ahmed and Mr Rasul and the actors who played them - Rizwan Ahmed and Farhad Harun - were detained at the Bedfordshire airport last Thursday after returning from Germany on an easyJet flight.
The charity issued a statement on behalf of Rizwan Ahmed that said he was subsequently interrogated by three Special Branch officers.
Mr Ahmed claimed he was asked if he intended to make any more political films.
Reprieve legal director Clive Stafford Smith said: "This may be a farce, but it is an ugly farce."
But Bedfordshire Police said officers were carrying out their normal duties.
The force said a man was stopped first by Special Branch officers having passed through immigration and three others travelling with him were stopped shortly afterwards.
It added the two remaining people in their party had already passed through the airport.
A spokesman added that no complaint had been made to Bedfordshire Police about the incident.
"Stopping and checking people in this way is part and parcel of police work both at the airport and across Bedfordshire as a whole," he said.
"Gathering intelligence and information under the Prevention of Terrorism Act and other legislation ensures we remain vigilant when it comes to preventing and detecting crime as well as providing reassurance to those people entering into and living in Bedfordshire and the UK."