> Of course, London has many green spaces and on the whole has plenty of trees, it's just they're quite unevenly distributed.

I would say they are pretty well distributed through places where people actually tend to live. I live in a pretty average residential area in zone 3 and not only are there nice parks nearby but there are plenty of trees. London is of course massive so I can't say it's the same everywhere but most residential areas I've visited have been quite green. The City and West End (very much commercial/touristy areas) are the exception in my experience.