An assailant armed with a knife has been shot outside the Houses of Parliament in London, and at least a dozen people have been injured on Westminster Bridge. The number of casualties is unclear. Stay up to date with the latest updates on the Westminster terror attack on our blog.

The leader of the House of Commons, David Lidington, said in the chamber that an assailant who stabbed a policeman had been shot by police. Amid confusing scenes, it appeared the incident may have unfolded in several locations, including the busy bridge where tourists often congregate to take pictures of Big Ben and other attractions. The incident took place on the first anniversary of attacks on Brussels in Belgium.