British police marksmen are being trained to confront Paris-style marauding gunmen in a bid to stop mass shootings of hostages, Scotland Yard has revealed.
Officers will "go forward" to engage with terrorist shooters even if it means leaving casualties untreated as the attackers are pursued.
The tactics were made public for the first time today after force bosses invited journalists to a training exercise simulating murderous gunmen storming a shopping centre, although the approach has been used since the Mumbai atrocities in 2008.
Assistant Commissioner Patricia Gallan, Scotland Yard's head of Specialist Crime and Operations, insisted that the force has no "shoot-to-kill" policy and said marksmen will operate only within the law.
"Every single set of circumstances has to be looked at on a case by case basis," she said.
"We know from the incidents in Paris and elsewhere, that the terrorists have taken a different tack in that they have been shooting hostages and such like.
"So the decision has to be made, and it is a brave decision at the time, about whether you stand back, in which case you may well have more people die, or whether the best thing is to go forward.
"And we've been training our officers to go forward. That is, going forward in the face of firearms and shots being fired at them as well as potential explosions and such like.
"We believe that is potentially what will save the most lives."
The mass shootings and bombings in Mumbai sparked the change in tactics used by counter-terrorism teams, and means that casualties may be left without first aid while the terrorists are stopped.
Ms Gallan said: "In asking them (officers) to go forward, we're asking them not to give first aid to people who are injured, and it might well be their colleagues as well.
"The most important thing is to actually get to the threat and stop them killing additional people, and that is why we've got to keep going forward and not tend to those that are injured at the time."
The number of armed patrols in London has been increased in the wake of the Paris attacks, and force bosses are considering how to get more officers trained.
Publicity of the training exercise was planned before the murders in France took place, and Ms Gallan hopes it will reassure the public.
"In light of Paris we still thought it would be appropriate to be open, to show what was happening and I hope it will reassure people that we are really committed to keeping the capital safe and mitigating the threat of terrorism."
Yesterday's exercise in the City of London was part of annual training for the Met's authorised firearms officers, of whom there are more than 2,000. It simulated a group of terrorists armed with guns and bombs storming a shopping centre.