Omar Deghayes has landed back in Britain.
The 38-year-old, whose family live in Saltdean, was arrested and taken from Luton airport to Paddington Green police station in London.
He has just returned from Guantanamo Bay where he has been held for the past five years.
A Metropolitan Police spokesman said he would be medically examined by a forensic medical examiner to ensure that he was fit to be detained and interviewed by police.
The spokesman added: "Inquiries are being carried out, as they must be, strictly in accordance with UK law."
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