Mayor of London Boris Johnson's request for water cannon to be rolled out on the streets of the capital is to be challenged in the courts.

The Police Action Centre (Pac) confirmed yesterday that it had been instructed to pursue judicial review proceedings against the decision by the Mayor's office for policing and crime (Mopac) to push ahead with the controversial plans.

Pac legal director Sophie Khan said: "Mopac had a statutory duty to carry out a public engagement process and to consider Londoners' views before taking any final decision.

"There are questions as to whether the 'engagement process' met the statutory requirements."

Mr Johnson was heavily criticised for announcing the controversial measure just before the Budget and allegedly rushing through a consultation on the issue.

The Metropolitan Police and Mr Johnson have argued that the weapons will be necessary to avoid a repeat of the riots that swept England in August 2011.

But opponents have retorted that the introduction of water cannon would lead to an unacceptable militarisation of policing.

Green London Assembly member Jenny Jones said: "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 bypassed informed opinion and pushed ahead with his plans to let the police have this weapon."