Problem now fixed!!
Simple one as well, we have a gravel drive way and a piece of gravel had found its way behind the bottom of the accelerator pedal. It wasn't easy to remove but it is out and all the power is back!
Thank f*ck for that, I couldn't see it the first time I checked as it was a black stone. I have been pricing up replacement pedals for the last few days, they aren't cheap but fortunately not required!!