Part of my life involves street homeless people, and some have addictions.
There is very little you can do for someone at that exact moment in their lives (beyond helping them inject safely which I wouldn't generally recommend)
It literally isn't the moment to try and approach someone.
Generally the police will just force them to get out out of public view, if they actually have the resources to attend in the first place. It's low down on the public nuisance spectrum.
I've just finished working last nights informal pop up street kitchen and community aid pitch night shift.
It keeps people of all levels of street living going, creates community and self help, and works to try to raise quality of lives, through everything from food and abscess care, to getting folk involved in writing and performance groups, and helps those who can be propelled upwards when they are receptive.
Every bit of what we use to provide services, comes from people who care.
We could do more if we had more. If you want to do something, make a donation (or volunteer) to any of the front line services trying to help people who are scraping through street survival. Most are operating on shoe string budgets.
There are huge numbers trying to survive on London's streets, some with severe substance addictions, most with broken MH, some just quietly broken, a few there by choice, and increasingly, working tent dwellers whose housing has gone, being sucked downwards.
Most are malnourished and winter's on it's way. Donate is the something you can do.