I have an X Reg TD4 Auto which has decided to blow out huge clouds of blue smoke when running at lowish speeds upto 30mpg round town. Not necessarily from cold. I was out yesterday and after engine warmed up after short drive about 3 miles, went into shop, then restarted it and plumes of blue smoke coming out of exhaust. There is no apparent loss of power so dont think its piston rungs or anything sinister like that. My mechanic has suggested EGR problem? Has anyone had this problem or suggest what could be causing this?

could also be a couple of valve seals gone, they tend to go hard then lift of the valve