Ok every now and then my vrs PD170 is a little lumpy at idle and hesitant on gentle throttle (its very happy when the taps are opened though)

Had the cambelt done, it made no difference.

had the injector recall done, no difference.

it's due a service and we're doing that next week, could it be fuel filter restriction?

I't had'nt flagged any faults up when we did the cambelt and I havent had any dash lights come up.

car is on 105800 miles now

Like you say, it could be a fuel filter restriction. Buy a new one & change it. Won't take long to do, won't cost much, and just might cure it.