Where is my nearest post box?

OK, so I’m lazy; I want to drop off a load of letters with a minimal amount of effort.

Now, for some bizarre reason, Royal Mail don’t have a Post Box finder on their site. All I can find is this page, which states:

Nothing could be simpler than dropping your mail into one of our Postboxes. There are 115,000 Postboxes nationwide, so wherever you find yourself, there’s one not too far away.

Cute. But why can’t you tell me how “not too far away” one is! You can tell me where my nearest Post Office is, so is it really that much more of a stretch to give me the closest postbox?

I wonder if there’s a social-networking-type website that maps out Post Boxes? I’m envisioning a Google Maps mash up type thing! Hmmm…

Update: Matt Bryce has created PostBoxr to help you find your nearest postbox. See his comment below for more details. I’ve added two post boxes in Cambridge already 😉