For some reason, bread in all its forms is a brilliant roach bait in running water, but is very inconsistent in stillwaters. The one exception is punched bread, which can be very good whatever the venue. Punch is, of course, just small pieces of flake, and I think its small size is the reason it works in lakes as well as rivers.
River roach, though, are much more willing to take a bigger bait, and a piece of fluffy bread flake the size of a 20p coin is ideal.
Feed is liquidised flake, fed either through a small open-end feeder or a tiny bait dropper to ensure it reaches the bottom quickly without first dispersing.