You may be referring to the circuit a couple of miles from Alton. I'm not sure if it was ever used for racing, but it is still used to give historic racing cars a run (which I assume are the Bamford's cars, as the estate where the track is located is in the heart of the JCB dynasty's world)
You can see the perimeter road to the lake in this link:
http://maps.google.co.uk/maps?f=q&hl...45319&t=k&z=15