- Video report by ITV News Security Editor Rohit Kachroo
A British man suspected of being a senior member of so-called Islamic State has been jailed for terror offences in Turkey.
Former London Tube driver Aine Davis was accused of being a member of 'The Beatles', the British Islamic State execution squad which included Jihadi John.
They are among those who beheaded hostages.
One former hostage, who spoke on condition of anonymity to ITV News, said Davis was the most violent among ‘The Beatles' - dubbed so due to their distinctive British accents.
He said: "He is the one who had the role of the punisher."
The hostage revealed he has now launched legal proceedings against Davis in his home country following a special court hearing.
Davis, who denied the charges, has been sentenced to seven-and-a-half years behind bars for being a member of a terror organisation.
In 2014, his wife Amal El-Wahabi became the first person in the UK to be convicted of funding jihadis in Syria. She was jailed for 28 months.
Last year ITV News revealed Turkish prosecutors had accused Davis of being "in charge of Daesh (also known as IS)".
They claim he slipped back into Turkey to plan a new act of terrorism.
The 33-year-old from west London was arrested in Istanbul last year.
The court case is thought to be one of the most serious ever brought against a UK citizen.
British aid worker David Haines was beheaded by Jihadi John in September 2014 and footage of the killing put online.
Mr Haines' daughter Bethany told ITV News she was "angered and disappointed" that Jihadi John's accomplice Aine Davis had only been jailed for seven years.
She said: "I feel that he should have been extradited back to the UK and put on trial to face his crimes.
"Seven and a half years is no punishment, compared to the suffering that the families of his victims have felt and will continue to feel.
"I feel let down by the justice system. At the very least he should have been locked up and should never see the light of day."