Well. The light is now fixed. It was a bit of a sod to find the fault.
The first thing I did was to remove the rear parcel shelf, so I could see the operation of the boot light. When the tailgate was up and the latch closed with a screwdriver, the boot light went out (as did the warning lamp on the dashboard). I pushed the lock button (so the light came on) and closed the tailgate. The boot light stayed on. Then I closed the latch and moved the tailgate up and down. Light goes off. Light comes on. Light goes off (You get the picture).
After pulling down the rubber tube thingy that connects the tailgate to the body, I find that some of the wires were scuffed. There had also been a previous repair (Not badly done though). With the damage fixed, I tried again. Good, but not perfect. The boot light went out 8 times out of 10. I did use the guide on this Forum to check out the latch switch. With a little bending and some cleaning, the switch works perfect! That's another job done!
Fitting a new exhaust manifold heat shield is going to be a swine. The Forum guide says it's a quick and easy job. One small thing though. The Rover used in the guide doesn't have air conditioning. I do. I've got this pipe that runs between the exhaust manifold and the radiator. This is going to be interesting......