So, I tried it again tonight and it was still doing the same thing. Noticed that the engine management light was on so presumed bike had gone into safe mode.
I ran it up to 70 degrees and switched it off. Left it for half hour and then tried again. Engine light is now off, bike revs fine, happy as larry.
I noticed that there is no built in diagnostic system on the hp4. I had a zx10 recently with diagnostics on the dash, not on the hp4 I take it?