The FBI has issued a special alert over a British man who took flying lessons in the United States illegally.
The FBI say UK authorities have been notified
Zayed Christopher Hajaig caused alarm when he sought to upgrade his pilot training at a flying school in Georgia before he had qualified.
The Atlanta Joint Terrorism Task Force has issued a special alert bulletin to police and aviation authorities.
It is believed Mr Hajaig, 35, fled to Britain when he became aware of the task force's interest in him.
The task force said Mr Hajaig "became aggressive and attempted to have the flight school accelerate his training schedule".
'Person of interest'
The FBI said UK authorities had been notified and he had been placed on a "no-fly" list.
FBI special agent, Steve Emmett, said Mr Hajaig "has been located in the UK and remains a person of interest".
According to customs officials, Mr Hajaig was living in the US illegally with no means of income and used calling cards to communicate with associates.
He has been described as a white British national who was born in Nigeria.
Two of the hijackers involved in the September 11 attacks reportedly completed part of their training at the same Gwinnett County Airport where Mr Hajaig took lessons.
Scotland Yard said it would not comment.
A spokeswoman said: "We don't discuss intelligence passed on to us from international agencies nor do we discuss individuals."