Cycle through to the Setup page, select Set Units, and change the Position Frmt setting from British to H D°M.M' (hemisphere, degrees, decimal minutes). While you're on that Set Units page, also make sure the Map Datum is set to WGS84 - that's the datum used for the deg/dec-minutes coordinates displayed on the cache pages.
Many Thanks, Munin
Will try it out over the weekend
Thanks again
Ben