I have this a few years ago with a vauxhall. When we looked at it at the family garage, we thought it was a fuel blockage in the swirl pot in the tank, but in the end a simple change of fuel filter fixed the problem.
I spoke too soon,it has happened again,my mechanic thinks it's a fault with the pump,he has rewired the earth and we are going to what happens,if it happens again after this I think it's going to be a new pump
Quite likely. Pump is immersed in the tank, if weak, is needing the head of fuel from a full tank to help. When down to half-full, pump is unable to pressurise enough. Wiring connections are unlikely to help, sadly.