In reply to Tall Clare:
Not that I wear specs, but personally I'd do the same as you. Not least because Lady Blue would tear my eyes out if I didn't.
However, if you're a bit of a cheapskate, who doesn't give a toss about your eyes, you can go and get an eye test done at a regular opticians. The actual cost of an eye test is about £75 (1), but the market won't stand that, so you get charged a lot less. That's a loss for the optician for starters.
Which they hope they'll recover through selling your glasses.
So you spend a while with the optician, looking through their range, seeing what works for you, etc.
However you actually make a note of the frame name and make, particulars, etc, walk out and go to an online site, and input all the details from your prescription, and order the glasses from the online site for a lot less than the optician would charge you.
Thing is, no-one is checking the fit of the glasses when they arrive, whether they are actually giving you the best vision (prescription changing obviously with distance from eye), etc.
It's a lot cheaper for you and the reason why many opticians - especially the small independent ones - are going out of business.
(1) If nothing else, the machines cost a *fortune*. Really a fortune. Hundreds of thousands of pounds.