Mayor of London Boris Johnson is pressing ahead with plans to buy water cannon despite accusations that he has ignored public opposition to the move.
Thousands of people contested plans to buy the machines for the Metropolitan Police during a public consultation by City Hall, as well as in online petitions.
But today Mr Johnson insisted the majority of Londoners backed the plans and cited the results of a survey carried out for the Mayor's Office for Policing and Crime (MOPAC) which appeared to show support.
Lawyers from advice charity the Police Action Centre have now been instructed to apply for a judicial review of the Mayor's decision to proceed with the scheme.
London Assembly member Jenny Jones said: "I am pleased the Police Action Centre is pursuing a judicial review against the Mayor's decision on water cannon.
"The Mayor has ignored the responses to his own engagement which were 59 in favour compared to 2,547 against water cannon.
"He has also ignored the detailed assessment published by the London Assembly, including members of his own Party and team.
"He has by-passed informed opinion and pushed ahead with his plans to let the police have this weapon.
"His engagement exercise - which may not have met the statutory requirements - showed that a majority of Londoners feel the Met Police has shown itself capable of responding to serious disorder, so why are we even talking about water cannon?
"I hope the judicial review makes the Home Secretary see sense and recognises that policing by consent requires building a political consensus.
"Water cannon has no place on our streets."
Water cannon have been linked to injuries including broken bones, and German protester Dietrich Wagner was blinded when he was hit by a jet from one of the machines.
Solicitor Sophie Khan from the Police Action Centre said: "MOPAC had a statutory duty to carry out a public engagement process and to consider Londoner's views before taking any final decision.
"There are questions as to whether the 'engagement process' met the statutory requirements."
In the poll for MOPAC, carried out by TNS, 4,223 people over the age of 16 were asked about water cannon, and 68% agreed that they had a "small, limited role" in dealing with "the most serious public disorder", meaning "the potential for loss of life, serious injury or widespread destruction to property".
Mr Johnson said: 'No-one wants to see water cannon routinely deployed on the streets of London but having carefully weighed up all the evidence, I have concluded there is broad support amongst Londoners for the use of this measure by the police in limited circumstances."
An independent ethics panel, headed by barrister Lord Carlile, will look at when water cannon should be used, if they are licensed by Home Secretary Theresa May.
She has already refused to provide central Government funding for the machines in London.
Plans are in place to buy three of the machines from Germany and then modify them for use on UK soil, at a cost of up to £300,000.