Can't say which is cheaper as I haven't seen UK prices for several years but my wife and I have been more than happy with the quality and price of spectacles here. There's a very wide choice of styles and prices with many, many shops supplying frames and lenses. I know of at least a dozen in Xania and there are almost certainly more than those I know of. What's more, those shops don't all stock the same styles.
The place we go to also gives high quality service and the owner is meticulous over fitting and has endless patience with advice when choosing appropriate frames.