you need to pull the cover remove the gears and look for any scoring and check tolerances. It could be that oil pick up screen is clogged up. We also need to know if you have GEMS or Bosch. Please add your rover info to your signature
so what are the pressures , how do you know its the pump it could be worm mains or big end bearings etc. hopefully its the pump but it may not be. try a thicker oil ,maybe your oil has thinned out from fuel ingress,might just need an oil change?
Ideally you want to add an accurate (mechanical) pressure gauge. You could plug it in to the port for the oil pressure switch. I've seen a description in Rave somewhere, but can't find it now.
Whatever you do, don't run the engine for any length of time until you're sure of the pressure!