In reply to Man city:
This may not be useful if you're already based out east, but the Arch in Bermondsey is a good wall that opens at 6am.
When I lived down there it was my go-to place, even coming in from 10 miles out, purely due to how much more pleasant it was at a quiet time early on. I can't comment for Mile End but at the Arch in the evening I found it wasn't great for training.
It was either having to constantly asking people to move from under the board/campus area due to them doing yoga, or people getting annoyed that you were doing more than a single circuit on the board and then jumping on whilst you were still going.
Though that may just be due to how popular it was. They began to operate a 1 in 1 out policy recently I believe and with one of their walls closing (they have 2 next to each other) this could be made much worse soon...