Gavin Brock has created an excellent overlay of the UK Ordnance Survey maps for the United Kingdom. The maps appear to be provided in several different detail levels which increase in detail as you zoom in.
Original Data From: UK Ordnance Surfey KML Content Created By: Gavin Brock’s Google Earth Hacks Access From: More . . . → Read More: Ordnance Survey Map Overlays for the UK