Thank you so much Dave and Trevor. The diagnostic people did plug it in and took it out for a run and said that it was high pressure fuel system problem but did not have a fix. One of the injectors was replaced as it had an issue but this just resolved the lumpy drive. I am taking the car to the garage that have looked after it for the past 7 years and I have a list for him to try:
Crank case breather filter, Diesel Filter, Pressure Sensor, Rail Pressure Sensor, Charge Airline from EGR to Inter Cooler, and I have added Low Pressure Fuel Pump
These are all suggestions from various people. About a month ago it was recommended that I put fuel additive in the fuel tank because of the lumpy drive, and this I did and I am now thinking that this may have contributed to the current issue.
Although the car is 17 years old, the bodywork is in amazing condition and I only do about 4,000 miles per year so I want to keep the car. It has done 89,000 miles and I am led to believe that this is not a problem for a diesel, and it is serviced regularly so I am hoping that it can be sorted!!
Thank you again for all your help and I'll keep you posted.