berlingo fuelling problem?

i have a 2002 1.9 diesel berlingo van, the other day when driving i noticed it wouldn't rev over 2500rpm, then as i got further into my journey, it wouldnt get over 2000rpm, then 1500rpm and so on until i couldnt drive it, it will now start then cut out after about 5-10secs, its in the garage at the moment and theres no faults come up on the diagnostics and theres fuel getting through to the fuel pump in the engine bay, my mechanic mate is suggesting the fuel pump has gone, any ideas as i dont want to fork out for a new pump if i dont need to, any ideas, it doesnt have the in tank fuel pump