There are chain pharmacies like Boots, where within a shop you can find "off-the shelf" products and a counter with proper pharmacists. And there are what we know as traditional pharmacies (chemist), though the later are not very popular and tend to be more expensive than the chains.

All the prescriptions obtained through the NHS have a fixed cost at the shops (unless you are under 16, a pensioner (men over 65, women over 60), or a student under 19 then you are entitled to free prescriptions.)

You can also receive free prescriptions if you are pregnant (or have had a baby in the past year), have a permanent disability or certain medical conditions (such as diabetes), or if you are on a low income receiving state benefits.

You can usually walk into the shop and they prepare whatever you need then and there, though sometimes they need to order special prescriptions and that can take a few days.