. Got both off side wheels off (and being fussy) gave them a good clean /look over only to find a 1/2 inch self tapping screw in the rear tread, no leakage but right through. 
luckily it should be repairable and Merit tyres is only 200 yards away 
Still it pays to check these things it could have let me down on the motorway. I'll now have to do the other side tomorrow.
