Cardinal Hordriss said:
I was wondering if older police boxes might predate Yale-type locks and keys
Indeed they did have different keys pre-1930s, and most used Skeleton keys instead of the Yale Type. We had a discussion on this very topic about the Glasgow boxes which span from the 1890, 1912, and then to 1930s and beyond with the Skeleton key type.
You can see the topic here: http://tardisbuilders.com/index.php?topic=8251.0
In Edinburgh they used Yale 5 Pin security keys, its a strange type. I have an example of one, and some photos of the originals.
The Police Boxes London used ETAS keys from 1930s to 1963. After that date Yale purchased ETAS and they ceased to exist as a brand. However you can find many examples of ETAS keys that evolve in design over the years. They start out fancy with diamonds and scrolls, then get more plain as they go along, or it may be the other way around. I've never quite worked it out properly. However I have at least four variations of ETAS keys marked for the London Metropolitan Police.
I have a few photo examples in the Relics section in my collection files here: http://tardisbuilders.com/index.php?topic=9034.0
Take a look, you aren't the only person interested in the locks and keys for Police boxes!