Thanks for all the replies.

It seems the vehicle was starting a regen and not completing.

I took the car for a good drive to get the engine hot and as I would slow down for junctions it would smoke and then as I accelerated the smoke would disperse , I then brought it back to the garage and put it on the ramp to check the DPF . Pulled out the rear temp sensor and checked the pressure feed pipework, all OK. Then decided to clamp the differential presure pipe and ran the engine and noticed that the pressure was building up slowly but on the next test drive I noticed that over 3 or 4 miles of brisk driving the pressure kept climbing up past 11kpa so took it back to the ramp and removed the clamp and the pressure immediately fell back to 1kpa or so.

On this experiment I am not sure why the pressure was building up as having clamped the rubber section of the pipe back to the sensor , I would expect no change as there is no back pressure from the DPF to the sensor. The other end of the sensor is open to atmospheric pressure . So not quite sure where or how the pressure differential could be coming from.

Whilst on the ramp I noticed that the rear temp sensor suddenly started getting hot and realised it was regening on the ramp at idle . The DPF got to 450 degrees on the rear and something like 260 degrees on the front sensor , it took several minutes before the regen stopped and rear sensor settled back to about 180 degrees. During this regen no smoke came out of the vehicle. After switching off the engine the DPF saturation fell to 52% from 125%.

Took it for a test and all was good no more smoke , no more regens and also the coil light indicating a regen was out.

The next day the garage on my advice decided to remove the DPF and it was soaked in traffic film remover for about 6 hours and then washed out with a steam cleaner for quite a while. Putting it back the immediate run poured out loads of steamy/smoke (not diesel smoke) for about 10 minutes and on another brisk drive this too cleared up completely. The DPF saturation was down to 8% but even after a short drive it still crept up to 14%.

Many thanks to Tony Attwood who took the time and trouble to ring me on the Monday and help me out with his advice and experience. We both agreed it must have been failed regens causing the smoke and possibly and oversaturated DPF not getting to the correct temperature to complete the cleaning and burn off the excess diesel. Tony suggested that the DPF should achieve at least 550 degrees for the regen to work .

I only got to 450 degrees on the rear sensor and it managed to complete the regen and put out the light but I suspect my earlier 'brisk' drive probably did the trick.

Time will tell.

By the way the engine never seems to run more than 77-85 degrees temp and max temp achieved at 2500-3000 rpm for quite a while when stationary gets me to 98 degrees before the fan cuts in. I think this engine may be running a bit on the cold side and this may have some effect on how well the regen completes.

Thanks again to Tony and all for replying

George