The Met is planning to buy three second hand water cannon from German police at an estimated cost of £200,000.
Speaking this morning, Boris Johnson said: "I have concluded there is broad support amongst Londoners for the use of this measure by the police in limited circumstances."
The majority of the 25 Assembly members - including Conservatives - are opposed to water cannon.
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Just off Fleet Street stands a famous tiered tower. Designed by Sir Christopher Wren, it became the inspiration for the wedding cake.
The president of the respected Royal Institute of British Architects became the latest high profile figure to enter the row.
The victim, thought to be in his 40s, was attacked in Bromley at around 11:30am. His condition is still unknown.