The last four British men held as terrorism suspects at Guantanamo Bay have arrived back in the UK, after almost three years in US custody.
The men were arrested and taken to a high-security police station
The men, one from Birmingham and three from London, were held after the US accused them of having al-Qaeda links.
The RAF C-17 plane carrying Moazzam Begg, Martin Mubanga, Richard Belmar and Feroz Abbasi landed at RAF Northolt in west London at about 1700 GMT.
They were arrested on arrival and taken to Paddington Green police station.
Protests have taken place outside the high-security station where the men are now being held, but police say they have to investigate why the four were originally detained.
The Pentagon has said they were freed after a request from the UK government, which had promised "that the detainees will not pose a continuing security threat to the United States or its allies".
Anti-terrorism officers, medical staff and two independent observers, including one Muslim, joined the four detainees on their flight from Cuba on Tuesday.
As soon as they had landed, a police van drove on to the plane, picking the men up and driving them to the central London police station.
Groups of protesters were chanting and waving placards outside the station when the men arrived shortly before 1840 GMT.
Some said the police were "giving negative feedback to the Muslim community and the wider community".
Muslim groups and lawyers for the men were united in demanding their immediate release.
The Muslim Safety Forum, set up after the 11 September attacks, said it had asked that the men be allowed to return home while the police carried out their investigation.
It said arresting them seemed like a political decision.
Massoud Shadjareh, from the organisation, said: "What sort of homecoming is this? They are innocent people."
Moazzam Begg's family has campaigned for his release
The Muslim Council of Britain said the priority should be for the men to receive counselling and medical help.
"We want these men to be returned into the arms of their waiting family," said Iqbal Sacranie, secretary general of the council.
Louise Christian, lawyer for Mr Abbasi and Mr Mubanga, said that after being "tortured and abused" at Guantanamo Bay, the men's arrest was "unfair" and "inappropriate".
Scotland Yard's Deputy Assistant Commissioner Peter Clarke said officers had talked to Muslim representatives and knew there were strong feelings about the case.
But he said: "The fact is that we have an absolute duty on behalf of all communities to investigate the circumstances leading to the men's detention.
"We are totally committed to ensuring that the men are treated properly and fairly."
The men were arrested under Section 41 of the Terrorism Act 2000, which covers alleged involvement in the commission, preparation or instigation of acts of terrorism.
They will be checked by a police doctor to see if they are fit to be detained and interviewed by anti-terrorism branch officers.
However they are not expected to be questioned until Wednesday.
It is believed the four will be allowed to see a relative, will have access to a lawyer and will be allowed a telephone call.
Five other British detainees were freed from Guantanamo last year and were released without charge after questioning by police in the UK.
Some later said they had been hooded and shackled to the floor in painful stress positions, and had witnessed beatings and other abuse during their time at Guantanamo.
The men were among hundreds of foreign nationals detained by the US without trial in the wake of the 11 September attacks.
Washington has alleged that all four released on Tuesday were "enemy combatants" who had trained at camps run by al-Qaeda.