I know you decided against them, but another vote here for the spd sandals. My favorite are the shimano ones because they are the most sandal-esque.
I'm in Houston, TX... much sunnier than the UK, and no problems with having to use sunscreen.
They are the best thing for the rain, dry uber quickly and if they are a little wet who cares, they feel great.
In the summer when I'm not using spd pedals, I wear my birkenstock sandals. It's the best way to ride.
I think you should give them a try.