Ok. Following on from removing all the fuses in the internal and under bonnet housings, and cleaning the contacts, and re-inserting them, Nothing has worked. Also removed copious multiway connectors, and sprayed contact cleaner liberally about. Still no joy. So decided to attack the Relays in the under bonnet fusebox. They all seem to be the same type MR538851 12VDC. Had to make a tool to pull them out. There was a small amount of corrosion on the legs, so did the usual cleaning, and re-inserted all 9 of them. Suddenly, the car works. Turned it off, had a cuppa. Turned it on, still works. Drove round the block, turned it off. Went mad and washed it. Turned it on, it still works. Currently off, and will see if it works tomorrow. Fingers crossed.