Willowman is right about the postman delivering 'junk mail'.
You can 'Opt-out' by telling the Post Office you want to opt-out of getting unaddressed mail delivered by the postman.
Check this link <
http://happenchance.co.uk/wp-content/uploads/2 006/08/royalmail_junkmail.doc >
Write a letter to the address given and they will reply, telling you lots of good reasons why you shouldn't opt-out, but be firm. You will then be sent this form that the Post Office will send and you just sign it and return. It takes about a month to operate. Even then, some will still slip through, but not as many as before. Good luck.