Have you heard of Freecycle? The Freecycle Network™ is made up of 4,927 groups with 8,252,662 members around the world. It's a grassroots and entirely nonprofit movement of people who are giving (and getting) stuff for free in their own towns. It's all about reuse and keeping good stuff out of landfills. Each local group is moderated by local volunteers (them's good people). Membership is free.
London has an active Freecycle group. I have been able to get some needed items over the years: a futon, an brand new weatherproof insulated vest, etc. And you can even post "wanted" ads...like the time I needed canning jars to make jam. It's a good way to get rid of items too, if you are decluttering.
The negative is, that you pretty much need to have a buddy with a truck if you need furniture. Posters are not going to deliver.
