Given the linkages a quick spray of WD40 and all seems to be well again, just need to find a dry day when i can get out for a spin..
I think i know what caused it now thinking about it.. just before the track evening I gave the bike a really good clean, including the chain and rear sprocket. They got cleaned with some muc off spray, i guess i must have got some on the suspension linkages 
If the pen is mightier than the sword then my keyboard must be a weapon of mass destruction ??