It was a bit of an exploration, but worth it in the end. At least I understand a whole lot more about ordering glasses, and the intricate nature of lens and frame sizes. There are things I've learnt or worked out in this search that have never been mentioned by any optician I've dealt with.
If your prescription isn't too bad (anything below 8 for Sph & Cyl combined), there are some good deals here if you go for a 2 for 1 offer. They won't touch me though!
http://www.glassesdirect.co.uk/style/retro/ 
