Any major high street will have probably three or four opticians, any of who will offer NHS sight tests for the £15 fee, You do not have to buy any glasses or contact lenses from them, just ask them to give you the prescription which you can use at any shop. As well as the reading tests, they will also examine your eyes and do other tests as appropriate. They will take a family history to look out for some problems (if you are over a certain age - 50 I think - and your parents had glaucoma you get the test free). You also get the test free if you are over 65 or in one of other exempt groups and some get vouchers to help pay for them. Cost will depend on the frames and type of lens and coatings you chose. Obviously if you need bifocals or varifocals the cost will be higher. There are several major chains and they frequently do special offers - one chain does a "two for one" offer, handy if you need reading and distance glasses (though you have to pay for coating the second pair) or at this time of year they do free light-sensitive lenses instead. Shop around for the best deal for you.

If they detect any problems they will either give you a letter for your GP or refer you to a hospital opthalmology department.