Is there supposed to be a spacer between the mechanical pump and the block on the A+ 1275? If there should be and there isn't would it result in fuel starvation because the stroke of the pump has been affected?

There should be a spacer/ insulator, if it's missing it's not just the stoke that'll be affected - the arm won't sit correctly on the cam so could cause all sorts of problems.

Thanks for that. There is actually one there but some manuals show it and some don't so thought I'd better check.

You need a gasket each side of the spacer too.

I've spent most of today removing the oil gallery plug that goes just above the timing cover (don't ask!) and when I stopped for a cuppa I went hunting for the fuel pump that came with the car. The original is half as big again as the one currently fitted (from ebay ) and there's no way that little pump is going to move as much fuel as the big one. So, once the engine is back together I'll refit the original if it still works (hasn't been used in years) and see if that helps. We live and learn, I suppose