Stop worrying everybody...
..And calm down Darren!
Sooo, only one thing for it, I decide to fit the new sender and try it wet.
I have a very nifty tool for syphoning tanks which is merely a tube with a ball valve at one end. You just poke the valve end into the tank under the fuel and jiggle it up and down. Very soon a column of fuel rises up the tube which is then lowered into the ready can and presto, out it all flows. So as planned I had the ignition on as the tank drained and would you believe it? The fuel light came on! It's always worked.
So I do now have a brand new fuel sender going spare if anyone has a need. Pm me for the price (It won't be the new price!).
So with the trip at 92 miles from last fill up (I'd run it low on purpose), I drained about 5 litres I would say. I have repeatedly recorded 68mpg from the old bird and always tried to fill up after no more than 100 miles, but it seems I have much more range than I thought.
I usually start to sweat at 120 miles thinking the fuel light doesn't work, but I must re-think this. Maybe I will take a ready can for a ride and see just when the light comes on and how far I go after that... Interesting.