Thanks all, this is exactly the kind of info. I was looking for.
I know what you're saying about the Trek bike. It looks good. (Too big for me but I'm sure there are more similar ones out there.) I've just got an idea that I would like a bike with a bit more character, and it would be nice to customise something. I prefer the look of thin tube steel bikes too. I'm looking at a Holdsworth 531 12 speed for £100 - maybe I'm crazy and that's not such good value? By the time I got a new cassette, back wheel, chain, STI levers etc., I wonder how much I would have spent? (any ideas?) And a cold set would probably be required too...