Footage shows the moment a King's Guard shouted at a tourist as she leaned in for a picture with him while he was serving his duty.

"Do not touch the King's Life Guard," he bellowed at her after he stomped his foot hard on the pavement outside Buckingham Palace.

The tourist appeared to be rather startled by the gesture, holding her hand against her chest while backing away.

This clip, which has since gone viral, has sparked a debate online about whether the King's Guard was justified in his response.