Mr al-Marris was held in Guantanamo for six years and eight months
A former Guantanamo Bay prisoner has been detained in the UK while on his way to see a human rights lawyer.
Jaralla Saleh Mohammed Kahla al-Marri said he arrived in the UK from his native Qatar on Sunday.
He was visiting lawyer Gareth Pierce, whose clients have included the the family of Jean Charles de Menezes, when he was held at Heathrow Airport.
A Home Office spokesman said he was unable to comment on individual cases.
Mr al-Marri is now at Colnbrook Immigration Removal Centre near Heathrow Airport.
The 37-year-old said British officials told him he was being held because he did not include details of his detention in Guantanamo on his visa application.
He said: "They kept me for an hour then said they were going to move me.
"They said I was going back to my own country. They said they don't want anyone from Guantanamo here.
"I said I was here in January and it was fine and if they don't want me here why did they give me a visa?
"There was no question on the visa about are you a Guantanamo detainee?"
Mr al-Marri was held in Guantanamo for six years and eight months before returning to Qatar in July last year.