Sussed at last. Rode the bike today for 10 miles with no issues. Then 5th gear 3000 revs and the dreaded stuttering started again. So for a couple of miles I thrashed her and then went to 3000 revs and pulled open the throttle really bad now. Pulled over to look around the bike to look for any clues. EUREKA!!! I was bending down on the left hand side when I heard a ticking sound. Looking closer and there was mega amount of sparking from the bottom rubber on No1 spark plug cap. People must have thought I was nuts as I was dancing around my bike at the side of the road. I pulled the rubber off and inspected the bottom of the cap for cracks. None obvious but I put it back on without the rubber. Started the bike up no sparks. Rode it for 20 miles, slowing down loads of times to less than 3000 revs and opened the throttle with no stuttering. Hurray. New NGK plug caps on order. darssi thanks for the info.
Is there a difference between SD05F and SD05FM (I was given this number by a bike dealer on the phone when I asked them which ones I needed for my bike).
Thanks to everybody for there guidance and input. I've learnt a hell of a lot about my bike from you guys and really appreciate it.
I did take a short video on my phone but don't think I can upload. But did take a picture and you can just see a spark on the rubber. In real time there were sparks everywhere.