Three water cannons purchased by the London Metropolitan Police Service (the Met) have arrived in the UK. They are now at a secret location being modified for use for the first time on mainland Britain. The purchase represents a new stage in the militarisation of British police.

The cannons cannot be deployed without a Home Office licence, which has yet to be approved. Last week, Home Secretary Theresa May said “there were several operational issues” regarding the use of water cannon and that she could not give a timeframe for her decision on whether to authorise them.

Once they are licenced, their deployment is then down to chief constables. Water cannons are part of an array of deadly weapons the police can deploy against protests and popular movements, including live rounds, rubber bullets, tasers, incapacitate sprays and policing techniques such as kettling.

With the backing of the Prime Minister’s office, Conservative London Mayor Boris Johnson last month gave the Met the green light to purchase the cannons from the German federal police. Contracts were exchanged at the end of June.

The “WaWe 9,” produced by the Ziegler Group and nicknamed “Mammoth” or “Goliath” by German police, was first introduced in 1982. It is named for its 9,000-litre tank capacity. This can spray water up to 65 metres at 18 litres a second, although some reports claim the machines can easily be adjusted to double the water pressure.

Johnson and the Met are trying to force an early licencing decision from the Home Secretary. In June, before the results of a health and safety assessment ordered by May, the Met went ahead and purchased the cannon.

Earlier that month, a spokesman for the prime minister said it was a matter of processing “licencing and regulation.” Johnson said he thought it was “highly likely” approval would be granted. He justified the rushed purchase on the grounds that “if we waited we would have missed the window to buy them for the very good price that we’ve got ...”

Johnson has downplayed concerns about purchasing the cannons ahead of licencing, saying they can always be sold if none is issued. He clearly intends to use them, however, and expects the Home Office will agree with him. He told a meeting of his Police and Crime Committee that the cannons “are being prepared for use in this country and obviously we await the certificate from the Home Office.”

Arguments that water cannon will be deployed rarely are belied by the experience in Northern Ireland, where they are already licenced. Between May and September 2012, they were deployed 53 times.

The Mayor’s Office for Policing and Crime (MOPAC) confirmed the purchase and some of the modifications, including the fitting of CCTV and “adaptations to bring them into line with the standards used in Northern Ireland.”

This underscores that the cannons have not been purchased to sit in a police compound but for mass repression. British companies have been exporters of water cannon, amongst other weaponry, to some of the worst dictatorial regimes in the world, and the state is fully aware of their purpose.

The public “consultation” process intended to influence the purchase and deployment was exposed by comments from Met Commissioner Bernard Hogan-Howe. Announcing that the cannon had arrived in the “last few days” he declared, “We have to have a period of training. A lot of officers to train. It’s going to take a few months before they are ready.”

At the Met, the officers being trained are from the Territorial Support Group (TSG) that specializes in public order containment. The civil liberties group Liberty, who have monitored the increasing militarisation of policing protests, have highlighted the TSG’s “inglorious reputation for heavy-handed policing and abusive and unlawful use of their powers,” noting that the unit “caused widespread outrage following its policing of the G20 summit in 2009 and the death of Ian Tomlinson which followed violent contact from a TSG officer.”

In a letter to the Guardian, Deputy Mayor for Policing and Crime Stephen Greenhalgh insisted that “Far from being lumbering machines, water cannon are as fast as fire engines,” adding that politicians should not get in the way of the police. “Senior politicians should think hard before denying the police the tools they need to do the job.”

The Mayor and the Met’s efforts to downplay potential deployment are a smokescreen for behind-the-scenes discussions on how to beef up the water cannon. Greenhalgh attacked concerns expressed by the Mayor’s former aides and some senior police officers, saying other police chiefs “are vehemently in favour of it and suggesting putting ‘SmartWater’ into the water cannons so they can identify people.”

Ultraviolet SmartWater stains the clothes of its victim so the police can round up protesters afterwards. It was used by the military in Afghanistan to identify insurgents outside the field of conflict. Similar measures have been used in Turkey, Indonesia, India and Zimbabwe, amongst others.

German pensioner Dietrich Wagner came to London earlier this year to warn Londoners just how lethal these weapons are. Wagner was blinded by a water cannon in 2010 during a protest in Stuttgart where another 100 people were injured. “Water cannons are not democratic. They are instruments of violence. They are considered much more harmless than they actually are,” he said.

He described events in Stuttgart. “The police surrounded us and used water cannon to threaten the demonstrators ... Ignoring their own rules and regulations for use, they blasted the water jet directly into my face, at a range of only 15 metres, and gradually increased the pressure. This smashed through my cheekbone and if the spray had continued for just one more second it would have hit my brain and I would have lost my life.”

In 1985, protester Günter Sare died after being stunned and then run over by a water cannon. The civil liberties organization Liberty has described the weapons as “inflammatory, militaristic and brutal.”

David Shaw is the West Mercia chief constable in charge of an Association of Chief Police Officers (ACPO) Home Office study into the feasibility of using water cannon, established following the 2011 riots in London and other cities in England.

In a briefing paper earlier this year, Shaw was also explicit that water cannon would be used on political protests. He wrote, “the ongoing and potential future austerity measures are likely to lead to continued protest ...” Deepening poverty, he continued, has “the potential, when combined with a significant (and often spontaneous) ‘trigger’ event, to lead to the outbreak of significant disturbances.”

At the London Assembly last January, discussing the 2011 London riots, Johnson provocatively urged police in any future disorder to “get medieval immediately on these people.” Water cannons will assist police to do just that.

Johnson specialises in flattering and fawning before what he calls the “hedge fund kings.” He defends the aristocratic principle that inequality is “essential” to the natural order. At one city dinner last November, he told the assembled financiers that their wealth was owed, not to any criminality and plunder, but to their superior IQ’s. To defend their plunder and its devastating social consequences Johnson is resorting to the methods of every outmoded, bankrupt and criminal elite—state repression.