By Ben Davies
BBC News political reporter
Armed undercover marshals could be deployed on London's Underground to foil future bombers, train driver union Aslef's boss has suggested.
Mr Norman: Marshals should be considered
Keith Norman said the marshals could deter terrorists, reassure commuters and back-up drivers after an attack.
He compared the idea with the US air marshals deployed to try to prevent plane hijackings in the 1970s.
Mr Norman, who says the idea is worth debating, stressed the marshals would have to be properly trained.
The Aslef general secretary also suggests a direct communications link between train drivers and the emergency services.
Mr Norman told the BBC News Website: "I would want to see people on there trained in security and possibly trained in the use of firearms so if they see someone who is possibly suspicious they can actually deal with that.
"But they look just like any other member of the public - you don't want someone in a bright blue Tube uniform who is easily identifiable.
"Ideally I'd like them to be able to help the train driver with carrying out procedures if anything does happen. The mayor of London certainly likes the idea of more people on the trains in a different capacity. You could call them Tube marshals or something like that."