In September 2015, when Sadiq Khan was campaigning to be elected London Mayor, he made a bold statement in an interview with the London Evening Standard: ‘I will do everything in my power to cut stop-and-search.’ He was referring to the policing tactic of stopping young men suspected of carrying weapons or drugs.

Mr Khan was echoing Theresa May, then Home Secretary, who in 2014 had instructed the police to scale down the use of stop-and-search after a Home Office consultation found that it was unpopular.

This change in tack has been followed by the most terrible consequences. In the past two years in London 141 people have been stabbed to death, according to figures from the police. That death toll is not so far short of the 179 fatal casualties suffered by the British armed services in the Iraq War, and I am sure that figure will be reached in the near future.

Year-on-year from 2015/16 and 2016/17 there has been a 31 per cent rise in knife crime and a 78 per cent rise in acid attacks in London, figures from the Mayor’s Office of Policing and Crime show.

A few days ago, some 19 months after he took office and in response to the massive surge in knife crime, Mr Khan finally changed his mind and announced: ‘Londoners will see a tougher crackdown throughout 2018. This will include a significant increase in the use of targeted stop-and-search by the police across our city.’

He made his statement after four knife murders in London on New Year’s Eve alone. Knife crime is out of control in the capital, and it was the received wisdom of the Left, which is evidently accepted by this Conservative government, which brought this about.

In 2014 Mrs May told MPs that stop-and-search was ‘unfair’ to black youths when it was ‘misapplied’. Her concerns were pure political class point-missing. She did not seem to grasp that the primary aim of stop-and-search is preventing murder. She instead spoke of strategies to reduce the policing tactic through ‘revised codes, best practice schemes and new methods of accountability’. It is important to remember that this droning jargon from the Westminster bubble must have been an aggravating factor in the deaths of some stab victims.

For his part, Mr Khan has long maintained that stop-and-search causes ‘community tensions’. This appears to be a way of accommodating a fact that politicians would like to avoid: some people do not want to be policed. I am fairly sure that if, for example, white middle-aged men started stabbing each other to death in large numbers that demographic would bow to an increased incidence of personal searches and conclude that it was for the common good. A public conversation might then begin about what was driving the fatalities. That public conversation never begins about the current knife problem. The middle-class metropolitan Left appears to look the other way from this ongoing slaughter of young people, preferring to bandy about the buzzword of the century, racism.

Some common sense is needed. It should go without saying that while it is unfortunate that some innocent young black men feel oppressed if the police search them, it is even more ‘unfortunate’ for other young black men to be stabbed to death because the police are told not to do their jobs properly on the grounds that some people are upset by it. Sadly, in a political environment awash in Leftist dogma, clear moral imperatives can become lost, as they have with knife crime.

As knife killings surged last year, Mr Khan spent £1.7million of taxpayers’ cash on the establishment of a Scotland Yard police unit to monitor ‘hate speech’ on Facebook and Twitter. As an example of wrong priorities, that takes some beating. But it seems that it is name-calling that vexes the Left, not sticks and stones or indeed knives.

The chief complaint about stop-and-search is that it disproportionately targets young black men. However, since many of the instances of knife crime occur among young black men, it would seem eminently sensible to patrol vigilantly in that demographic. It would surely save lives, and that is the whole point. The Left do not agree. They prefer to talk about ‘education’, knife wands and knife arches outside schools. Wands and arches are designed to detect knives in the manner of airport scanners, and needless to say those outside schools will not play a part in policing older knife carriers. These measures smack of institutional defeatism and fiddling while Rome burns. With the situation being so desperate in London, perhaps knife arches are a practical measure, but they would also be glaring evidence that in 2018 the police cannot, or have been prevented from, controlling the problem of schoolchildren carrying knives in the capital city of an allegedly advanced country. It would also be further evidence of the lethal consequences for a society when traditional authority and morality is overturned.

It is encouraging that the London Mayor has made a sensible change in policy. But it comes too late for the families of the 80 people stabbed to death in London on his watch in 2017.