The London Bridge attack and a similar one in March may have been shocking, but authorities have known for years that such incidents were coming, NBC News reported.
Last year London's police chief warned it was a case of "when, not if" the U.K. joined the other countries to be hit by terrorists.
Despite that, more than 90 percent of the capital's police officers carry out their daily duties without a gun. Most rely on other tools to keep their city safe: canisters of mace, handcuffs, batons and stun-guns.
The Metropolitan Police, which covers most of London, was founded in 1829 on the principle of "policing by consent" rather than by force. They believe police officers with guns sends the wrong message to communities and can actually cause more problems than it solves.
The Metropolitan Police carried out some 3,300 deployments involving firearms in 2016. They didn't fire a single shot at a suspect.