May said the weapons should not be used as a part of riot control techniques, citing safety fears as a major factor.
In the House of Commons this afternoon, she said:
Where the medical and scientific evidence suggests that those powers could cause serious harm, where the operational case is not clear, and where the historic principle of policing by consent could be placed at risk I will not give my agreement.The application for the authorisation of the Wasserwerfer 9000 water cannon does not meet that high threshold.
However her ruling comes months after London mayor and MP for Uxbridge and South Ruislip backed the use of £218,000 of government money buying three German water cannon.
May said she "remained unconvinced" about "the operability" of the water cannon that were purchased by the Met, which are 25 years old.
Without safeguards they have capacity to cause harm.
We believed allowing police the option of deploying water-cannon, even though they would be seldom seen and rarely, if ever, used, was a sensible precaution which would allow us to deal with a number of specific public disorder situations more safely and effectively than we are currently able to.
As Met said we will maintain and train on them and apply again in the unlikely event of major threat to public order #askboris @luke_oxlade— Mayor of London (@MayorofLondon) July 16, 2015
Boris sitting behind Theresa May as she humiliates him by announcing he cannot use his expensive water cannons pic.twitter.com/VsadMXAFnd— Isabel Hardman (@IsabelHardman) July 15, 2015
As well as the water cannons, Boris also ordered 100,000 promotional t-shirts. pic.twitter.com/lQdlNcpT7w— General Boles (@GeneralBoles) July 15, 2015
Meanwhile, Liberal Democrat mayoral hopeful had this to say:
The Mayor must apologise to London taxpayers for his foolish and costly actions.
Still, it's one rule for parts of the UK and a completely different one for others.
Water cannon have not been ruled out for use in Northern Ireland, and in fact were deployed in Belfast on Monday against loyalist demonstrators during the Orangemen's annual celebrations for the commemoration of the Battle of the Boyne.