The map that AlanM has posted is what NATS has published, and is actually a doctored map of all three sectors - west, east and north - with the north sector removed. However, NATS forgot to add the bit in the north we already do back in to the map.
So the coverage of Farnborough Lars west still follows the circle to the north and north east, out to 30nm, and doesn't stop at the M40 as indicated.
Sonic