This week Sadiq Khan revealed that three redundant water cannon, bought controversially by his predecessor, are to be put up for sale, with the proceeds going towards helping to tackle gang crime.

It is a decision I totally endorse and welcome.

Back in 2014 Boris Johnson decided to purchase three second hand water cannon from Germany.  We now discover that £322,834 of taxpayers’ money has been spent by the Met Police on purchasing these 25 year old vehicles, and then transporting, fitting out and repairing the machines.

The scale of the foolishness, and quite frankly arrogance, in purchasing these water cannon is hard to underestimate.

For a start these water cannon were purchased before authorisation was given for their use by the Home Secretary.  After they had been purchased consideration of permitting authorisation of their use was undertaken by the then Home Secretary.  It was firmly refused.  On this issue Theresa May showed immense thoroughness in carefully examining the merits for and against the adoption of water cannon.  Her statement to the House of Commons on the 15^th July 2015 is an example of a Home Secretary acting in a truly professional way.  The Hansard record is well worth a read.

But rushing ahead and purchasing water cannon before getting Home Office approval was not the only error made by Boris Johnson.  At City Hall the London Assembly Police and Crime Committee carefully examined the issue.  Our investigation involved extensive evidence being taken.  Our cross party report was very clear that there were strong arguments against adopting water cannon.

When we examined the issue it was obvious that there were very serious risks of injury to innocent people from the use of water cannon.  Indeed there is extensive international evidence to confirm this, as can be seen from the US to South Korea.   Not to mention Germany, the very country Boris Johnson purchased the second hand water cannon from.

However, there were many other arguments against their adoption.

There are, for example, real limitations on how they can be used, especially in many parts of London.  In giving evidence to the London Assembly, Sir Hugh Orde (then President of the Association of Chief Police Officers and someone with experience of water cannon in Northern Ireland) stated:

They are a complicated bit of equipment. They are big. They weigh tonnes. They do not move quickly and in fact, when they do move, they take a lot of stopping, rather like a fire engine. They weigh a lot, so it is not something that can whizz around any city. They would not whizz around London.

We were told that they would not have been suitable for use in the disorder in Tottenham in 2011.

We even heard of occasions when their adoption might be counter productive in dealing with public disorder situations.

On the London Assembly it was not just Liberal Democrat, Labour and Green Assembly Members who urged the Mayor not to proceed with purchasing water cannon, but a number of colleagues from his own political party.  When the issue was put to a vote of the whole London Assembly in a motion I proposed, the vote was 20 Assembly Members against adoption of water cannon, with just five backing Boris Johnson.  A number of Conservative AMs voted in favour of my motion.  These included Kit Malthouse (now Conservative MP for North West Hampshire) and James Cleverly, (now Conservative MP for Braintree).

So Boris Johnson thought he could pre-empt the Home Office in dictating policy on the use of water cannon in England and Wales.   He also thought he had no need to listen to the views of the London Assembly, including members of his own party.  He even admitted that he hadn’t bothered to read the London Assembly Police and Crime Committee report on the issue.

As on many other occasions, Boris Johnson attempted to make fun of the whole situation.  Appearing on LBC and then before the London Assembly he even promised to be blasted by a water cannon to demonstrate their supposed safety.  A promise, of course, he never kept.

As a London Assembly Member for eight years I have witnessed many similar incidents of Boris Johnson deflecting examination of a serious issue with a mixture of humour and ridicule of his opponents.

Humour certainly has an important role in politics as in life, but now that some of the huge errors and blunders made by Boris Johnson are becoming clearer by the day it is time to realise what a grave error so many media commentators have made by not taking him seriously, or scrutinising his decisions.

Kevin Spacey in the film “The Usual Suspects” uttered the line “The greatest trick the devil ever pulled was to convince the world he didn’t exist.”

I am tempted to say that in UK politics the greatest trick Boris Johnson ever pulled was to convince so many people that consequences from his actions don’t exist.

* Caroline Pidgeon is a Liberal Democrat London Assembly Member and Deputy Chair of the London Assembly Transport Committee