Hi Trevor....welcome to the Forum
It could possibly be a vacuum leak as this causes similar symptoms.
If you carry out an exhaust gas check (any MOT approved garage should be able to carry out a Pre-MOT gas test) and look for Oxygen (O2) levels above zero which suggest a leak in the intake or exhaust.
Also, Hydrocarbons (HC) which should be very low (almost zero) which suggests that there is an ignition problem if high.
Let us know how you get on with it.
Cheers, Trevor