You may be interested in my answer in a related thread

http://www.reddit.com/r/AskHistorians/comments/29oe97/how_did_mail_work_in_the_1500s1600s/

I also recommend exploring the Royal Mail's Timeline http://www.royalmailgroup.com/Timeline

and the British Postal Museum Archive http://www.postalheritage.org.uk/explore/history/