Thanks for all the answers guys... I'm 99% sure the disc is fine. I haven't crashed yet so I can't see any reason why it would get warped... I had warped discs last year and the feeling was totally different...
I think my problems started when I did the 2 changes below (unfortunately I did both in the same time and so don't know which one could be the cause of my problem):
- fitted a 6.5kg spring to my Ohlins rear shock (instead of a 7.5) following the advice of a mate.
- fitted a pair of jacks (built by Rich @ Louigi Moto) to raise the rear of the bike.
Anyway I'm not tired, so I'm now off to the shed taking the forks apart, I need to see what's inside
(I've even been suggested that they could be empty of oil in regard as how they behaved in static... ).