Hi Hadrian, Glad you got it sorted, I just found this, I looked the other day but couldn't find it. Maybe of some use to others for the future because these P38's are not going to get better.
Remove fuel supply pipe from fuel filter. Place end into a container. Remove relay R12 (engine bay). Connect positive feed to terminal 5 of relay housing for exactly 10 seconds. Note quantity of fuel dispensed, minimum should be 180ml in 10 seconds this will confirm satisfactory pump delivery.