Forgot to add that the current folder on the device containing the maps "Western_and_Central_Europe_2GB" does not match any of the 965 map folder names of what I've downloaded. It's hard to determine what to replace the maps with if the folder name doesn't match. To be honest I'm more than happy with just the UK on this device and the option of one for California (Western USA).
Here's what I've got downloaded that are close enough maybe for a direct replacement for the UK maps:
Central_Europe_West_965_7250 (+ version 7280)
Europe_1GB_West_965_7280 (+ version 966_7404)
Europe_West_965_7250 (+ versions 7252, 7280, 7283, 966_7372)
Western_Europe_1GB_965_7280 (+version 966_7404)
Western_Europe_965_7250 (+versions 7251, 7252, 7283, 7372)
United_Kingdom_and_Republic_of_Ireland_965_7250 (+ versions 7251, 7252, 7280, 7282)