@John Bayly

Sussed!

They guess the region you are interested from ip address. I'd have thought that it might have occurred to the developers that as I'd gone to the trouble of typing .co.uk they might be able to glean some sort of clue about the map I'd like to use. Seems to work well for Google! I forget that Microsoft's geeks always think they know what's best for you ;-)

There's always Streetmap I suppose. It's always been the best for coordinates anyway.

...and Open Streetmap is looking VERY promising too.