Are You Smart Enough to be a British Postman?

Gregg Ross at Futility Closet posted this envelope.  According to the addressee, "Though not having a single written word upon it, this envelope reached me from London without delay."  Can you figure out the address?

Solution is at http://www.futilitycloset.com/2011/06/19/torturing-the-post-office/
Enjoy