2.0 DCI M9R engine poor cold start

Our Laguna II ph2 has the 2.0dci engine and it is really struggles starting when cold, the engine turns over fine but its as though only one or two cylinders fire up and it takes a few seconds for the others to catch, this producers white/grey smoke. First off I checked the glow plugs and found 2 of them completely failed so replaced all 4. The problem remained. I have tried the primer bulb and whilst there is occasionally air in it the car still struggles to start. I have also tried cycling the ignition to repeatedly heat the glow plugs and this makes a difference some times but not often. I have read for error codes with a generic reader and there was an old stored code associated with the failed plugs but that has not returned and there is nothing else.
Any help?

2.0 DCI M9R engine poor cold start