This summer could see water cannons deployed on the streets of mainland Britain for the first time ever, according to official letters between the Mayor of London and the Home Office.

Senior officers at the country's biggest police force are seeking to take delivery of the controversial crowd dispersal weapon within months to deal with possible outbreaks of disorder similar to the riots that hit London in the summer of 2011, sparked by the police shooting of Mark Duggan.

In a letter sent on Monday by Boris Johnson to Home Secretary Theresa the Mayor of London confirmed that the move by the Metropolitan Police came as a direct result of the riots, and that there be “short period of engagement” over the introduction of water cannons before a formal decision is made next month.

Until now water cannon have only been made available to police in Northern Ireland where they were introduced to quell public disorder during the Troubles and six vehicles are still used to tackle crowds using blast bombs and throwing missile.

In his letter Johnson writes to his fellow Conservative: “Following the disorder in August 2011, both the Metropolitan police service and Her Majesty's Inspectorate of Constabulary stated that there are some circumstances where water cannon may be of use in future.”

He added the Metropolitan Police commissioner, Sir Bernard Hogan-Howe, has made assurances that water cannon would be “rarely used and rarely seen”.

The decision to authorise the use of water cannon on the British mainland rest with the Home Secretary, who is facing calls from critics to halt steps towards the militarisation of the police and halt a slide towards the stifling of the democratic right to protest.

It is not known how many vehicles the Metropolitan Police is seeking to introduce but each water cannon is understood to cost in the region  £1.3m and require a dedicated staff of 20 as well as 180 further specially trained officers,

However the letter confirmed that a request for Government funds for the equipment has been rejected by May, leading the Mayor's office to confirm that the water cannon will funded by an allocation from the Mayor's office and be solely for the use of the Metropolitan Police.

Jenny Jones, a London Assembly Member for the Green Party said, “Allowing water cannon on the streets of London is a step in the wrong direction towards arming our police like a military force, and it goes against our great tradition of an unarmed police service. People have a democratic right to protest and my fear is that once the Mayor allows these weapons onto our streets we will see them being used against people exercising their legal right to protest.”

A spokeswoman for the Mayor's Office for Policing and Crime said: “Since the riots in August 2011 the police and the independent Inspectorate of Constabulary have argued that water cannon should be available as one of a range of tools to respond to serious public disorder.

"This is supported by the vast majority of the public. MOPAC will now be undertaking a period of public engagement to get the views of Londoners, prior to any final decision to purchase water cannon."

A Home Office spokesperson said: "We will ensure forces have the tools and powers they need to maintain order on our streets. We are currently providing advice to the police as they build the case for the use of water cannon."