Well, I didn't even know this - I normally write England/Scotland on the last line.

"When sending mail to UK addresses we need a full and accurate address complete with postcode. You do not need to include a County name provided the post town and postcode are used. Avoid using commas or full stops and do not centre or stagger your lines."

From this site: http://www.royalmail.com/delivery/ma...sing-your-mail