This morning getting the car out of the garage I noticed a strong smell of petrol. There was a small puddle on the floor on the o/s.
Sump was dripping fuel which was coming from the central gasket on the pump. Opening the inspection hatch I dried it all up but it became wet with petrol again. I managed to tighten the bolts (six?) holding the top to the bottom of the pump- all about half a turn. It was dry from then on, and I've just driven two hundred miles and it's still dry.
As the material used in pump diaphragms ages its gets brittle and shrinks a little and so it sounds like the pump diaphragm needs changing at the least, Although a new pump might be the better/easier option in the long run as the operating cams can wear leading the poor performance.