You’re posting an article by someone with eccentric views on a lot of topics and an anti-multiculturalist agenda to advance. (For example, they believe that Rishi Sunak is not English.)
Not sure about the UK, at least in Canada it's poverty/people being broke. More homeless people and the general harassment they inflict on people in their surrounding area, more petty crime that the police don't bother investigating so people don't bother reporting it. More theft from grocery stores, more petty scams for <$1000 &c.
One reason homicides are down is because hospitals have got better at keeping stabbing victims alive. Stripped of context it looks like a win. Put in context the question becomes, why are there so many stabbing victims? Gang crime, etc.
Also, hospitals have got better at treating knife injuries in lots of places, not just London. This would not explain why London has a low homicide rate per capita compared to lots of other cities.