Anti-terrorist police arrested a man Tuesday in connection with the attempted bombings of London's transit system on July 21.
The man was arrested at Gatwick Airport as he got off a flight from Addis Ababa, Ethiopia, Metropolitan Police said.
The 23 year-old is suspected of the commission, preparation or instigation of acts of terrorism. He had been out of Britain since June, police said.
Fifteen people have been charged in connection with the July 21 attacks at three Underground stations and on a double-decker bus.
Those attempts came two weeks after four suspected suicide bombers killed 52 bus and Underground passengers in London's worst terrorist attack.