The father of a former High Wycombe grammar school pupil, who is believed to have joined ISIS and whose name featured on a list of jihadists held by Turkish authorities, told national media he regretted buying his son a mobile phone, claiming he was “brainwashed” through the internet.

Shabazz Suleman left Wycombe’s prestigious Royal Grammar School [RGS] in May 2014 when he went on exam leave for his A Levels, and is believed to have joined ISIS in the same year.

According to national reports, he wants to return to the UK to “face justice”.

His father Afzal Suleman reportedly told MailOnline his son was radicalised on Twitter, adding that he felt sympathy for the people who join the terrorist group.

He is alleged to have said: “...this is what young kids do [when they] see people being killed, being gassed.”

In an interview with The Times this week, Shabazz allegedly said he is “desperate” to return to the UK after becoming “disillusioned” with jihadism.

He is thought to have left ISIS and is believed to be in the hands of Turkish militia.

In 2014, his name appeared on a list of 180 ISIS hostages being held by Turkish authorities in exchange for 49 of their diplomats.

Mr Suleman is reported to have told national press that he has had intermittent contact with his son, who he does not believe has killed or tortured anyone.

He is believed to have said: “The biggest mistake I made was buying a phone for him. He was in his bedroom on it all the time.

“You don't really keep an eye on their phone. I believe [his radicalisation] was through Twitter.”