Word of the threat came as three men from Leeds were charged with helping the four suicide bombers plan the subway attack that killed 52 people, The Telegraph reported Friday.
Thursday's charges against the trio followed nearly two years of investigation by Scotland Yard's Counter-terrorism Command.
Detectives pieced together hundreds of hours of footage from closed circuit television cameras showing the suicide bombers and their alleged accomplices conducting reconnaissance of London landmarks and the Underground system.
The bombers are thought to have changed their plans at the last minute.
"I firmly believe that there are other people who have knowledge of what lay behind the attacks in July 2005," Peter Clarke, head of the police
counter-terrorism command, said. "We need to know more about their movements, meetings and travel."