It is worrying that the Mayor of London Boris Johnson appears to have carried out little debate – in public at least – before providing an ‘in principle’ rubber stamp for water cannons – warns Joanne McCartney

“Rarely seen and rarely used.” This has become the Metropolitan Police’s stock phrase to downplay public concern in London about its attempts to secure three second-hand German water cannon by this summer. In a report by the London Assembly Police and Crime Committee, published this week, we have questioned whether this reassurance is valid.

The Met’s position appears to have changed during the engagement process, which is being managed by the London Mayor’s Office for Policing and Crime – or ‘MOPAC’. The original case for water cannons – prepared for the national debate by the Association of Chief Police Officers – identified only three examples in the last decade when water cannons may have been considered as a tactic.

All were in London: the Countryside Alliance march in 2004; the Gaza demonstrations outside the Israeli Embassy in 2008; and student protests at the Millbank building in 2010. However, the Mayor of London Boris Johnson told us in evidence that he would not have wanted water cannons used in these instances – and stated that such use would have been “counter-productive” in the student protests.

As it scrabbled to find convincing examples of how water cannons would be used, the Met referred to other incidents when officers faced a scale of disorder that might have justified their use. At a public event hosted by MOPAC, the Met discussed the carnival against capitalism in 1999; the disorder in Tottenham during August 2011; and violence between fans connected to a Millwall versus Birmingham football match.

This was despite the fact that the Met’s own report into the riots had concluded that a water cannon “is unlikely to have been an appropriate and practical option owing to the speed and agility of the disorder” and the ACPO case had described their use in such instances as “limited”. We had also heard earlier assurances that water cannons would not be used at football matches. At the same meeting, the Met said they had had identified one or two incidents a year when water cannons could have been considered as a tactic. While he sought to contrast this to the 1,500 major events the Met police deal with each year, most would agree this exceeds the likely interpretation of “rarely seen and rarely used”.

Of course, police officers often make a professional case for new equipment or legal powers. Many officers speak passionately about needing the tools to deal with those who want to commit harm. But it is down to politicians to ensure these tools are really necessary for the protection of the public. In our investigation of the Met’s roll out of weapons, we said that MOPAC should act as a visible critical friend when the police request expanded availability of weapons.

This would necessarily involve informed and transparent debate. It is worrying then that the Mayor of London Boris Johnson and his office appear to have carried out little debate – in public at least – before providing an ‘in principle’ rubber stamp for water cannons. Furthermore, if weapons are made available, it is politicians who must ensure they are used appropriately and do not lead to a creeping infringement of our rights.

Joanne McCartney is chairwoman of the London Assembly Police and Crime Committee