Armourtex in Hackney are excellent. They had so many hipsters getting their bikes powder coated (so they'd fit with their overpriced apartments' aesthetics when parked in the hall) that they opened a specific cycle shop, which they now seem to have moved to Hackney Road as it outgrew the tiny place in Rowe Lane. They coated my 80's 5-speed Brompton, which are nororiously finicky, serviced and rebuilt it better than new.