In case anyone else has a similar problem it was still a fuel pump issue. The pump was replaced with a recon and had the intermittent issue.

Got the pump tested by a diesel specialist and they found that the valves on the pump were at fault. When the car got warm the pressure was dropping off over time - it needed about 140 psi to start and it was dropping below that in the fuel rail when warm.

Fitted new valves and the car works fine!!! 2 month nightmare.