Update.
I have checked glow plugs with a glow plug analyser courtesy of a neighbour. They all come up as ok although I did notice a couple took a few seconds longer to get there.
Checked oil and its bang on max and no signs of head gasket failure. As said earlier though, I can’t say if its PD engine specific.
Suppose next step is to drop the oil and change oil and fuel filters?
Car always starts instantly. Just with a cloud if white smoke and the clatter roughness for a few seconds when it’s cold.