Spot on mate 😀. I did some more searching and couldn't find a definitive answer on if the learned values need to be reset when the sensor is changed so I just changed it anyway.
So to sum it all up, just the sensor replacement fixed the issue in conjunction with clearing the faults (plus a couple of test drives with a scan after each to check, and for my own sanity).
I did note after the swap that the old sensor was noting the DPF differential pressure @14psi constant and an offset value of 0.9psi. after the swap the new Sensor was noting the DPF differential pressure @0.1psi at idle which obviously then rises as you put your foot down as I would expect, also the offset dropped to -0.4psi but not sure how or if that is even relevent.
So now it's fixed and been out for a good run, I've seen an instant 18mpg increase (calculated not from dash).
So I'm now a happy chappy and it only cost £26 from my local autofactors 😀.