loads of things can contribute to this, mine does it but a good long run at high speed ussually clears it out, when i say long run I mean at least 50 miles of 80 and above, mine then dont smoke for at least a couple of weeks,
however oil an filter can make a difference as said above airfilter, but sounds like you have a slightly sticky wastegate or something, possibly a boost leak, and until the turbo can pressurise the system it will be running too much fuel, also fuel type can make a difference, try all different brands, but supermarket fuel is usually the worst for smoke, my money is on a boost leak somewhere though 
I thought about it being cheap

(if that's possible) fuel, as i use tesco because of the points.
As far as i can fathom, it shouldnt be any different, as Tesco buy their fuel from big refinery names.
It might be a case that bigger names add different additives? who knows.
I have yet to try a different brand recently, but i will for the next tank and report back.
That still doesnt solve the turbo "stall" i feel when driving.
I have driven a few turbo diesels, and this is the first one that feel like it almost pulls back before pushing forward....it's an odd sensation.....
I thought boost leak, and did identify one, but it seems not to have helped.
Is there somewhere i can plumb in a temporary boost gauge with a t-piece? as i have one of those hanging about somewhere.
Would be interesting to see what it's hitting (which will also help when i come to do the adjustments to the wastegate at somepoint soon.,
With regards to a sticking wastegate....should i spray some maintenance spray on it or something?
And lastly, where are the common boost leak hot spots if anyone knows?
thanks