David you may not get 2.5 Bar when testing the pump in situ.
Do you have a problem apart from the LP pressure fault code? As Brian said just about every diesel plugged in to a T4 will throw up this code as it is generated every time the ignition is left on and the car not started.
If you look at this sketch you can see that fuel from the ITP not supplying the UBP can return to the tank via the restrictor valve and that can bleed off pressure.
If your ITP can be heard with your ear next to the open fuel filler cap (unplug the UBP if you need to) then chances are it is supplying the correct pressure for the system.
If you have a problem with the engine cutting out or running in limp mode them you could have a problem with the pipework in the tank or a blockage somewhere.
.