Boris Johnson has said he wants to buy water cannons for use in tackling violent disorder.
The canons, which critics say can cause blindness and broken bones, would need to be licensed by the Home Secretary, Theresa May, before they can be used in the capital.
The Mayor of London has announced he wants to purchase three cannons from Germany at a cost of £90,000 .
The move is supported by Metropolitan Police Assistant Commissioner, Mark Rowley, who told the BBC: “When protestors’ obvious objective is attacking a fixed location such as Parliament then you’ve got a small group of highly violent people, posing a lot of risk to the public.
“In those situations it’s potentially a credible tactic.
“We’re not going to use it against a small number of violent people in the midst of thousands of peaceful people. We’re not presenting it as a silver bullet for all serious disorder.”