These are the passport-style photos I took for my Permit to Search the Thames Foreshore. The foreshore is the expanse of riverbed or beach that is exposed by the fluctuation of the tides. In the UK, most tracts of foreshore (and beaches and estuaries and so on) are owned by the Crown Estate (more or less by the Queen).
People known as mudlarks — historically often children, the infirm, or criminals — have been scavenging bits of treasure or usable stuffs from the river for hundreds of years. In theory, anyone can walk down the foreshore during low tide, but you need a permit to detect or dig.
Here’s a short vid of an American Garrett representative (I think it’s Garrett’s son, actually) detecting on the Thames foreshore: http://www.youtube.com/watch?v=rDoSnHNM5Zg
If you were the Queen, would you give a permit to someone looking as scruffy as I do in the photos? True mudlarking style!