Mrs HH - apart from the bit about it not running on petrol, the problem with Herc seems remarkably close to one I had with Garp - that got steadily worse until I just stopped at a traffic light.
Land Rovers and pets - designed to be an embarrassment at any opportunity!
In my case it was a badly fitting low voltage connection on the coil. It would be fine for days and then just die, run, die, run...
In the end I discussed it with the serial disser in the post above, mentioned what I had discovered when it died at the lights and changed my mind from a possible fuel problem to an electrical one.
Rather than use the easily dis-connectable crimps on the coil wires I now have lugs on there and the wires are bolted to the coil.
No problem since.
