Little update here...
I made a start on stripping EGR side of things down on saturday but only got it finished today.
EGR cooler removed, blown out with airline, no real issues with that.
EGR valve removed, inspected, smallest 'chink' of light around valve seat - nothing worth talking about - cleaned anyway for good measure.
Re-assemble, and as expected no change.
MAFM still reads 450- 475ml/stroke, car still drives fine except for the smoke.
Pretty much at the end of the road with it. Clearly there is a DPF problem, still getting limp mode due to high pressure in exhaust. So DPF must be blocked.
Removed the pre DPF pressure hose from the sensor, and managed to drive considerable distance without getting limp mode, the code P0472 was logged - pressure low, but this didn't cause limp.
Found some play in turbo spindle so going to suggest the original garage has a look at
1. Sort the DPF out
2. Address turbo spindle play
I'm satisifed that its 'electrically' sound. I think