Response (rather belated!) to:

"Anyhow - on the subject of your UK grid, I notice that you have only given the facility of reading off a grid reference for the point in the centre of the map. Thus to get a reference, one has to guess where the middle of the map is, and then move the terrain until the spot one wants a reference of is right in the middle, before then activating your middle of the map reference feature. Is there a way to get the mouse pointer to read off the map reference alongside the lat and long that appear at the bottom of the GE screen? "

All you need to do is double-click on a placemark to centre it. The centroid grid ref then becomes that of the placemark.

Alan