Yep our "Post Codes" as we call them are made up of letters and numbers.
London is based on which part
Others are one or two letters, one or two numbers (depending on the size of town) and then one number and two letters.
The beginning part eg, CR3 relates to a particular town, the last three a group of buildings on a particular road.
Have a look at www.royalmail.com
if you are interested (or not!)