A British nurse who contracted the Ebola virus in Sierra Leone arrived at a London hospital on Sunday, the ministry of defence said.
The patient, who is not "seriously unwell" according to the Department of Health, was evacuated from Sierra Leone to London in a military plane.
The Briton is the first person from the country to have contracted the virus in an outbreak that has killed at least 1,427 people in West Africa since March.
The Department of Health said the patient was evacuated in a specially equipped C17 Royal Air Force military plane to RAF Northolt in north west London.
Flanked by a police escort, a special military ambulance took the man across London to Britain's only specialist Ebola isolation unit at the Royal Free Hospital.
His bed will be sealed off with a tent with its own ventilation system, and only specially trained staff can enter the unit.
A spokesman for Sierra Leone's health ministry, Yahya Tunis, said the man was a volunteer nurse working in Kenema in eastern Sierra Leone, one of the areas hardest hit by Ebola which has now been quarantined.
"His colleagues are very sad over the development as he is considered as a valued member," Tunis said, adding that he was involved in "surveillance, contact tracing and the burial of Ebola victims".
England's deputy chief medical officer Professor John Watson insisted that the risk of the virus being spread in Britain remained "very low".
"UK hospitals have a proven record of dealing with imported infectious diseases and this patient will be isolated and will receive the best care possible," he added.
Ebola spreads through direct contact with the blood or bodily fluids of an infected person.
The Ebola epidemic has spread through Liberia, Guinea and Sierra Leone, while Nigeria has also been affected. It is the worst outbreak of the killer virus yet.
The World Health Organization has warned it could take several months to bring the epidemic under control.