Aircon working like a charm now. Shunting refrigerant through at 0.4 Deg C!
I did not need a pump after all. The regas was justified because it had not been done for years, but that was not the cause of it not working. There was 8 bar in there, so definitely no leaks.
It was my main cooling fan all along. I had not noticed that it was not working, and it needs to work for aircon to work.
It turned out that one of the plugs feeding power to the fan and corroded and crumbled into nothing.
I checked the pump by putting 12v directly to it, and the clutch activated fine.
I rewired the plug to get the fan working, and in turn the aircon started working.
Because I thought it was the pump, I bought one, and typically for me it was the wrong one. I bought another which was correct and got it fitted.
I tested the original after it had been replaced, and it worked! I did not know I could put 12 v direct to the pump to test it.
So I have 2 fully working aircon pumps to get rid of now, along with a few other parts bought in error.