Home secretary Theresa May has refused to allow the Metropolitan police to use water cannon, despite London mayor Boris Johnson having spent over £200,000 on buying the vehicles.
The home secretary was also concerned that water cannon on the streets of London would destroy trust between the police and the general public.
Water cannon have always been banned from UK streets, aside from Northern Ireland.
May insisted this should continue, saying: "This country has a proud history of policing by consent and this is a decision that goes to its very heart."
Last year Johnson took the decision to buy three water cannon from the German police without clearing their use with the Home Office.
Now London owns three second-hand water cannon that it cannot deploy.
Jim Waterson is a politics editor for BuzzFeed News and is based in London.
Contact Jim Waterson at firstname.lastname@example.org.
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