Boris was sitting behind Theresa May in the House of Commons as the Home Secretary announced that she would not be giving permission for the Metropolitan Police to deploy three second-hand water cannons in London.

She added that she remains “unconvinced as to the operability of the machines under consideration”.

A water cannon’s full blast could cause “spinal fracture, concussion, eye injury and blunt trauma”.

Scotland Yard bought three of the water cannon second hand from German police past year at a cost of more than £200,000.

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.

Mrs May also referred to an incident in Stuttgart, Germany, in which a a 66-year-old protester was completely blinded by a similar model of cannon.

We haven’t forgotten that Boris Johnson agreed to be blasted by a water cannon. “It is a police tactic that has not been used in Great Britain previously and there are those who argue that its introduction would change the face of British policing”.

“They are 25 years old and have required significant alterations and repairs to meet the necessary standards”.

“While evidence suggests these water cannon are unlikely to result in serious or life threatening injuries… the assessment nonetheless poses a series of direct and indirect medical risks from their use”.

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”.

She also said she was “acutely conscious” of the potential impact of water cannons on the public’s perception of police legitimacy.

“The country has a proud history of policing by consent and this is a decision which goes to its very heart”, May said, presumably thinking that any device that can rip off the skin of someone it is pointed at might not be the best of ideas.

“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.