Kurdish forces captured Anwar Miah in Deir al-Zour province a month ago, the BBC reported on Sunday.
A video of his capture has surfaced on Twitter and shows Miah saying he has lived in Syria for nearly four years.
It is believed he is being held in a prison in northern Syria, guarded by US special forces.
In the video, Miah is blindfolded and says he has been working as a medic in IS territory for the last four years.
"I'm a qualified pharmacist from the UK. I've been working in the hospitals since I came," he is heard saying in the video.
At least three other British men who are accused of being members of IS are currently in Kurdish and US custody in Syria.
They include two Londoners, Shafi El-Sheikh and Alexanda Kotey, who are alleged to be members of the notorious group dubbed the The Beatles. The pair were captured in January.
US officials believe the cell they belonged to beheaded more than 27 Western hostages.
(This story has not been edited by Social News XYZ staff and is auto-generated from a syndicated feed.)
