LONDON (REUTERS) - Prime Minister David Cameron's government has refused to allow water cannons to be used on the British mainland, arguing that the crowd control weapons, which police said were needed following riots in 2011, could destroy public trust.
Water cannons, which either douse crowds with spray or emit a more forceful jet, have regularly been used across Europe and in Northern Ireland to quell public disorder but never in the rest of the United Kingdom.
Critics say they would cause irreparable damage to the image of British police, whose officers are still mostly unarmed and patrol the streets as "bobbies on the beat".
But following days of riots in London and across the country four years ago, the country's worst disorder for years, police chiefs and some politicians including Cameron called for the cannons to be made available.
Last year, London Mayor Boris Johnson ordered the purchase of three 25-year-old second-hand machines from the German Federal Police at a total cost of £218,000 (S$440,000), but they could not be used without the consent of Home Secretary (interior minister) Theresa May.
May, who along with Johnson is a front-runner to replace Cameron when he steps down before the next election, told parliament on Wednesday she had refused to authorise their use.
"I would hope this decision will be welcomed by many people," said May.
She said her decision was based on concerns about the injuries they could cause, their limited effectiveness, and fears that their use could change the face of British policing, damaging the public's trust.
"Where the medical and scientific evidence suggests that... (they) 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," she said.
Cameron himself had suggested water cannon could be used during the 2011 riots but Hugh Orde, the former president of the Association of Chief Police Officers, told Reuters at the time they would have been "entirely inappropriate and more importantly entirely ineffective".
May's decision is an embarrassment for Johnson, who said his decision to buy the vehicles was taken with the strong support of Cameron and London's police chief.
"I do think it's the wrong decision," he told BBC TV, adding that if there were an outbreak of violence in the future, the police could present a new application to use them.
"Nobody wants to see them used. I accept that... there's something a bit un-English about it. The question is, do you keep them... in reserve as a utensil of crowd control that the police might want to call upon?"