OK, For those like me who have some experience with these sort of engines, but not enough to confidently take an injector apart, here's how this was resolved....eventually!
I did get a great deal of helpful advise from the camelot-forum.co.uk where there a number of off griders lurking. I took the injector over to Asher's in Southampton, injector specialists, and it tested fine. I returned with the pump, and the manager hand tested and said it looked almost new and thought it also was ok. He thought an airlock in the pump was the cause. Well, I had bled every orifice imaginable, but he said it would need pressurising with a pump. I bought an outboard squeezy pump and managed to attach it to the fuel line and squeezed fuel through the filter, pump and up to the injector. With the injector inverted and connected, I could see that no fuel was spraying from the injector. Crazy. After several days of trying this and that (suggestions included hitting it with a hammer while pumping, new pump, etc etc, One of the guys said that I should unscrew the top of the pump and remove the plunger, pump through some fuel and replace. By now I thought there was nothing to loose (the exploded diagram shows about 20 parts inside the pump, horror). Anyway, after reassembling, amazing! she eventually spluttered into life!
Well, I guess the moral of the story is not to let an ST run out of fuel, they can be an absolute nightmare to get going again. It's crazy that there is no shut off valve from the fuel tank, you have to pump the fuel out of you want to change the fuel filter. Diesel pours straight into the sump when messing around trying to bleed the darn thing! The joys of living off grid!

OK update, there was no fuel coming  through the injector, but was gushing out of pipe when slacked off. I have
taken it over to PB Asher in Southampton who repair injectors and also have a new one in stock. I should know in a couple of days whether it is the injector or not. (the sun has finally come out and is now merrily charging with the panels!)

We are off grid and this is our back up generator. I bought it 6 years ago with 40 hours running, it had hardly been used. She's done about 500 hours now without a hiccup. a couple of days ago, it ran dry for the first time. I bled the fuel filter and the exit of the fuel pump, but it just will not start. I have taken off the rocker cover and turned it over with the injector fuel pie disconnected and fuel appears to be coming out. it's electric start and vapour is coming out of the exhaust, but no hint of a firing. Anyone have any suggestions? I was thinking of a squirt of easy start to jolt it into action....

Mike

IOW