Alan,thanks for the input have scoped both the regulator and pressure sensor for duty cycle and voltage together with the current draw which seems to vary proportionately with the increase in rpm.

The duty cycle is in spec between 20-40% the current set value is 1308ma and actual value is 1331ma.

The voltage from the rail pressure rises from approx 1.31v to 1.89v at 3000rpm with the fuel pressure rising from 300bar to approx 600bar at 3000rpm.
When road testing the fuel pressure increases as expected on acceleration until I reach approx 30/40mph foot to the boards the engine man lights flickers and the vehicles stalls with no disproportionate pressure rise or fall and will start up immediately with no problems.

What is noticeable is a heavy crackling from I assume to be the injectors when the vehicle starts to struggle.

Finally have checked the max output from the pump by cranking with all injectors and regulator disconnected which produces approx 1200bar within 10 secs.What am I missing ??