Finally discovered what the occasional heavy smoke is on acceleration and idling.
The symptoms are as follows:
The car starts to judder slightly at idle, as it used to do when the DPF was starting to regen.
On acceleration there are massive clouds of thick smoke coming from the exhaust which carries on at idle. This stops when i turn the ignition off and restart it.
The 'dealer' was supposed to have removed the DPF because it was faulty but it is clear to me after closer investigation that the ECU thinks it is still there and therefore pumps raw diesel into the exhaust, causing the thick horrid smoke.
If I get a remap, will I be able to get an add on part that maps the DPF out of the ECU as its really really annoying now!!