It seems most of the pistons are pretty sticky, only one was moving the way it should and that was in the right hand side calliper and the pads on that side have a white edge wear pattern hence the warped disc. I am out of seal grease so will have to rebuild them tomorrow, it looks like I have found the problem, the dealers would have just replaced the discs and passed the mot and then the issue would have been back next year, in fact that is what they did last time as I let them swap the discs that time. Always better to do it yourself.