The Ridgeback looks to have better parts but is more exensive so that's where the extra $ are going. The Cannondale however is a better known brand though so is the "safer" choice and may have better resale. Both are going to be solid entry level city/hybrid bikes and I think your decision to avoid suspension is wise as it doesn't work very well in practice but adds complexity, weight, maintenance issues and cost. The difference between 7 or 8 speeds is not so much the extra gears which around town are not really needed but 8 (or higher) indicate better quality parts. This means they will last longer, need less servicing and after a few years will maintain their feel.
I'm not UK based but here are some other UK bike sellers whose names pop up frequently:
https://www.evanscycles.com/
https://www.wiggle.co.uk
https://www.chainreactioncycles.com