Thanks for the replies.
Checked the plugs (well the one I could easily reach), it says NGK IR so guess that's right.
It's coming up for its 12 month service, only done about 1800 miles this year, been busy. So nothing changed.
Have re-adjusted the TPS. Did follow the guide that stated you wanted the line to move to the top as soon as you start to twist the throttle. That is now set to around 2500 rpm.
That is where it was weird. As I was setting the sensor the revs picked up, it did this a few times as I tried to hold the throttle steady. Then the revs went to 4000 without me moving anything, I let go of everything, and it eventually dropped to tick over, then back to 4000, then tick over, then 4000, All without me touching it. I nudged the TPS again and it settled back down. It did this a couple of times. I eventually turned it off and gave it some time to cool down as it was getting hot by then. When I returned was able to set it fairly quickly.
I'm guessing this means the sensor is a bit temperamental and could do with replacing. If so where do I get a replacement sensor, they don't seem to be on fleebay.
Did take it on a test ride of course. Tried your suggestion of using 4th at 30mph, and it did improve the jumping, though it did feel a bit alien I can learn.
What it didn't help was going through a 3rd gear corner, just drop the throttle that little bit too much and then pick it back up, it gave a little jump that certainly made sure you were awake and made my a r s e grip the seat.