Hi all, well the guys at the MB Shop had my Sprinter back in on Friday 30th May and replaced the fuel line and it starts fine now (it was after they replaced the o ring) so the problem was the fuel line and O ring were damaged when fitted at MB when the van was built but has taken nearly three years for this problem to arise.
I hope if anyone else has this problem what I've found may help.
How they picked up on the problem was, I left the van with them overnight and they hooked it up to the computer before they tried to start it. When they did start it and it stalled the computer told them there was no fuel pressure, so they knew where to look from there.
Happy motoring.
Mike (Richo 1953)