After some googling I discover that there's a bug in the 2.2 and 2.2.1 OS releases that treats the UK regional settings as metric (not as a mix of metric and imperial). It's an odd approach, and not one I'm happy with. Surely mapping conventions are to use the distance measurement prevalent in the country that's mapped, not the regional preferences of the user?
What I want is a mapping application that uses kilometers where they're used on the roadsigns, and miles where they're used. After all, it's those roadsigns that will help me make the actual journey.
Is that too much to ask?
Ah well, the Windows Mobile device we use as a GPS is charged now, so I'm going to use a real mapping tool. Time to fire up CoPilot.