Boris Johnson must be expecting a spot of bother soon.
For the London Mayor is moving ahead plans to get the UK's largest police force water cannon ready in time for the summer.
Johnson has written to Home Secretary Theresa May to say that he will ask members of the public and key figures about their views on use of the machines "in the most extreme circumstances".
An "engagement" process is due to begin this month and a final decision by London policing authorities over whether to proceed is expected in February.
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It would then be up to May to decide whether to licence use of the machines, which it is hoped will be available for police in London by the summer.
She has rejected a request for the Home Office to pay for the Met's water cannon as a national asset.
There are plans to buy three cannon from Germany at a cost of £30,000 each, that will then need to be modified for use on UK soil.
Johnson told May he was "broadly convinced" of the value of having the cannon available, but added: "Should the engagement plan reveal serious, as yet unidentified, concerns I will, of course, take these into consideration and share them with you before you make any decision to licence this non-lethal tool."
The machines have reportedly caused serious injuries including to a German protester who was blinded in 2010.
Last year nearly 3,000 British police officers were trained how to work around the cannon before being deployed to Northern Ireland as part of the massive security operation for the G8 summit.
Water cannon have been used in Northern Ireland for some time, but not on the UK mainland.
May told delegates at the Police Federation last year that she was considering requests from a number of UK forces to use the machines.
London Assembly member Jenny Jones said: "Would the Mayor have supported the deployment of water cannon against students protesting against their fees going up?
"What happens if the Commissioner wants to deploy water cannon but the Mayor doesn't? Londoners need to know when and in what circumstances the Mayor would agree with the Met using this weapon.
"Allowing water cannon on the streets of London is a step in the wrong direction towards arming our police like a military force, and it goes against our great tradition of an unarmed police service. People have a democratic right to protest and my fear is that once the Mayor allows these weapons onto our streets we will see them being used against people exercising their legal right to protest."
If the Home Secretary allowed use of the machines, an ethics panel chaired by Lib Dem peer and barrister Lord Carlile would look at when and how they should be used.
A spokeswoman for the Mayor's Office for Policing And Crime (MOPAC) said: "Since the riots in August 2011 the police and the independent Inspectorate of Constabulary have argued that water cannon should be available as one of a range of tools to respond to serious public disorder.
"This is supported by the vast majority of the public. MOPAC will now be undertaking a period of public engagement to get the views of Londoners, prior to any final decision to purchase water cannon."