Britain's last remaining Guantanamo Bay detainees arrived back on UK soil tonight, and were immediately arrested by anti-terrorist police.
But the men, who were kept in legal limbo as suspected terrorists at the American naval base on Cuba for up to three years, were arrested on board the flight shortly after it landed.
Scotland Yard said the men were being held under Section 41 of the Terrorism Act 2000, which refers to the "alleged involvement in the commission, preparation or instigation of acts of terrorism".
Deputy Assistant Commissioner Mr Peter Clarke, head of the Anti Terrorist Branch, said: "We have discussed this case with members of the Muslim community and recognise that there are strong feelings about the return of these men to the UK.
"But the fact is that we have an absolute duty on behalf of all communities to investigate the circumstances leading to the men's detention. "Our inquiries are being carried out strictly in accordance with UK law and procedures.
"These have built-in safeguards and are subject to independent scrutiny. We are totally committed to ensuring that the men are treated properly and fairly." In a statement, Scotland Yard said the men would be transferred in custody by police to a central London police station and medically examined to ensure that they were fit to be detained and interviewed by officers from the Anti Terrorist Branch.
It added: "Each man would be allowed to make a phone call and have access to a solicitor of his choice. "Due to the unique circumstances of this case each men will be allowed a visit by a family member."
PA
The four - Mr Moazzam Begg from Birmingham; Mr Feroz Abbasi from Croydon, south London; Mr Martin Mubanga from Wembley, north west London; and Mr Richard Belmar from St John's Wood, north west London - landed at RAF Northolt in west London at 5.02 p.m.