// what is after all, a mainly black problem. //
No it isn’t.
It is a nationwide problem, and affects all communities.
Knife crime is bigger in the capital because it has more people. And in communities in London like Haringey, which is largely a black area, surprise surprise, the victims and perpetrators are mainly black.
But stabbings occur all over the country, in places with a lot fewer black people. North West England and the East Midlands combined have a similar number to London of stabbing crimes.
There are over 45,000 incidents a year, and just looking a London will give you a very distorted picture of what is actually happening. I realise that a distorted picture is useful to people who want to promote a certain agenda.
Some good info here
https://www.bbc.com/news/uk-42749089