What is the difference between a ring circuit and a radial circuit?

It as simple as the name implies ring circuit ,it 's in the circular form that is from the panel to the outlet and back to the panel . While radial is from the panel and stop at the out let without going back to the panel.But note that in a ring circuit you must use 6mm cable and 32/30 amp fuse rated.

Ring-main circuits must be wired using 2.5-mm2 cables, not 6-mm (whatever that is) cables.