Police will not be able to use water cannon to control serious public disorder, Theresa May has announced.

The Home Secretary said she had decided not to authorise forces in England and Wales to deploy the Ziegler Wasserwerfer 9000.

The move could pave the way for a row after London mayor Boris Johnson approved the purchase by Scotland Yard of three of the cannons second-hand from German police last year at a cost of more than £200,000.

Mrs May rejected a formal request from police leaders for the cannon to be made available nationwide which was lodged in March last year.

She told the Commons her decision was based on medical and technical issues raised in expert reviews, while adding that she is "unconvinced" by the "operability" of the machines under consideration.

The Home Secretary said that while evidence suggests that the cannon are unlikely to result in serious or life-threatening injuries, medical and technical assessments had posed a series of "direct and indirect medical risks" from their use.

"These include the possibility to cause primary, secondary and tertiary injuries, including musculoskeletal injuries such as spinal fracture, as well as other serious injuries such as concussion, eye injury and blunt trauma," she said.

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.

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

They are 25 years old and have required alterations and repairs to meet necessary standards, she said.

A probe by the the Scientific Advisory Committee on the Medical Implications of Less-Lethal Weapons (SACMILL) found 67 separate outstanding issues which would need to be addressed before they could be deployed, Mrs May added.

She also said the devices have limitations, particularly in "fast, agile disorder", while claiming their use could be "entirely counter-productive" in areas with a history of mistrust of the police.

Mrs May said: " The decision on whether to authorise water cannon is a serious one.

"Water cannon, without safeguards, have the capacity to cause harm. 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.

"This country has a proud history of policing by consent and this is a decision which goes to its very heart.

"But 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."

Following the announcement, Mr Johnson said he does not "necessarily agree" with Mrs May's decision.

Mr Johnson previously offered to be sprayed by water cannon in order to demonstrate they are safe.

However, he denied "playing politics" in endorsing the purchase of equipment before it had been given the green light by the Government.

Mrs May and Mr Johnson are seen as two of the leading contenders to succeed David Cameron as Conservative leader.

Water cannon have never been used on the British mainland, although they have been deployed in Northern Ireland.

Calls for police to have access to them first emerged in the light of the riots in 2011.

Scotland Yard later concluded following the disturbances that there could be a role for the tactic and police later submitted a formal request for the Home Secretary's authorisation.

Questioned about concerns about the state of the machines, Mr Johnson said: "I'm told they are perfectly serviceable and would do the job very well."

He said he respected the "care and thoroughness" Mrs May had taken in coming to the decision.

However, he said it was "curious" that the reasons given by the Home Secretary "don't seem to apply to the people of Northern Ireland".

The London Mayor told Sky News the cannon would keep the cannon previously purchased "in reserve", adding: "If there is another occasion in which life and limb and property is at risk and police really do need to make use of that utensil then it will be open to them to apply again."

In a statement, the Metropolitan Police said: "We fully respect the Home Secretary's decision but we are naturally disappointed.

"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.

"We presented our evidence to the mayor. He supported our request, and funded the purchase of three vehicles.

"Our officers have been able to train with these for several months.

"This has been of significant value in developing our understanding of how to deploy the vehicles and what tactics we should adopt in the very rare event of extreme disorder.

"However, we understand that any changes to the way police are able to use force in any scenario must be very carefully considered and we know the Home Secretary has applied detailed scrutiny to the evidence before coming to her decision.

"Metropolitan Police Officers occasionally travel to Northern Ireland to support their colleagues. This can require them to deploy alongside water cannon.

"We will be retaining our devices to ensure our officers are properly trained for this eventuality.

"This will also give us access to equipment that is already used elsewhere in the UK, but only on specific political approval, as is appropriate, and one that is likely to be granted only in the most extreme of circumstances."

Asked whether Mr Cameron was happy with the decision, the Prime Minister's official spokeswoman said he had always made clear there was a process that had to be followed.

"There is a clear process for a decision. That's for the Home Secretary to make and he respects her decision. The process has been followed," the spokeswoman said.