Hi Andy:
Yeah, that's a known issue. The problem is this: You have to specify at the time you upload the custom POI database whether the speeds and units of measurement are metric or imperial. Sadly, you can't have both.
The only ways to work around this are as follows:
1) You reload the custom POI's whenever you cross the English Channel, and when you are doing the reload, you specify the measurement units of the place you are going to (UK or Continent). This is what I do, but it means you need to have a laptop computer with you.
2) You need to talk with the folks who are constructing your database, and ensure that they use the same measurement units (metric or imperial) for the whole darn custom POI database. It's fine to have speed cameras loaded in with the trigger points specified in km/h, and have the GPSR set to display MPH - in such a case, the GPSR will do the conversion from km/h to MPH, and warn you at the appropriate speed. If you had such a database, then you would specify that it was constructed with metric units when you upload it using POI Loader.
The root cause of the problem is that the folks who create the custom POI databases mix units of measurement in the database - they list UK speed cameras with MPH trigger points, and Continental speed cameras with km/h trigger points. This forces you to follow procedure 1), above.
Michael