Thanks for the advice guys. The Ridgeback was way too small for me, but the Carerra felt right so went with that. It feels suprisingly light and much smoother to ride than the borrowed Bianchi I've been on. I've taken it round the local community bike place to measure the chain with a cc-32 checker thing, and it failed on .5 and .75. What would be a suitable quality replacement chain for this type of bike?
I also measured the chain on the more expensive Bianchi I borrowed, and it failed the .5 test, and almost the .75 test, so I guess that needs replacing too before I give it back. Again, what would be a suitable chain/price for a £500 bike?