Hi,
On some of the older lift pumps you could strip them down and clean out, it sounds like the NON RETURN valves in the lift pump are leaking back , or you have a small leak.
I assume you mean you have to prime the pump only not actually bleeding the pump or injectors.
Try cleaning out the lift pump, you don’t need to remove the lift pump just the top, if that doesn’t work replace the lift pump.
Is this vehicle new to you? I have seen some non complete Diesel conversions (not quite getting the fuel system correct ) causing problems.

Hi, tahnks for that - i've had it for about the last eight months but it's been getting harder and harder to start (Needing to draw fuel for longer and longer). But i don't think the pump itself is leaking, it might have a lot of crap in it though because i've just replaced the fuel tank which was pretty bad internally...
I'll take the top off the lift pump and see what its like inside. Otherwise i have been priming the injector pump, but not the injectors in order to get it to fire. I was just talking to a fella in the motor factors who suggested fitting a one-way valve on the fuel feed, just outside the fuel tank.
I'll keep you posted on how i get on, thanks again - Pat