I love geeky stuff like this! The Royal Mail (formerly Consignia, formerly Royal Mail) has a page on their website all about about how to clearly address your mail.

An envelope requires only five lines if addressing somewhere in the UK:
- Line 1—The addressee’s name.
- Line 2—Building number and street name.
- Line 3—Locality name (if required).
- Line 4—POST TOWN (print in capitals).
- Line 5—POSTCODE (print in capitals, in full, on a separate line).
Important points to note:
- You do not need a county name (e.g. Fife) if you use the post town and full postcode.
- No commas or full stops.
- Left-align your address, do not centre or stagger your lines.
So now you know. Although you probably use email and Twitter, don’t you!