If you are in the North of England, I can't recommend The Reptile Room near Blackpool enough. Great staff and a massive variety of snakes of all kind. It's specifically a privately owned reptile shop so they know a lot about the care of snakes (as opposed to a more generalised brand name shop like Pets at Home). I also recommend Urban Jungle in Manchester and The Reptile Wonderland.

All good shops with nice animals, great reviews and friendly staff, from my experience.