I managed to get the truck to a commercial garage .
The truck will only start - drive when the fuel regulator is disconnected .
At idle the truck has low fuel pressure , I've seen the fuel pressure above idle say 1500 rpm & the pressure at the high pressure pump stays the same as at the common rail when at different rpm's .
The garage checked the injectors & there ok .
The low pressure fuel pump is also ok .
They want to check a sensor on the common rail ( low pressure sensor I think )
They said it might be the high pressure fuel pump but aren't completely sure & are really nervous about changing it incase it's ok .
The mechanic looked on a forum & found someone else had a canter that wouldn't start when the fuel pump regulator was plugged in .
I suppose there's still a chance it may be the ECU although the garage says it's really rare for a ECU to break .