was driving to inters yesterday car was running perfect stopped in derby at mcdonalds after that car ran like sh!te wouldnt boost past 0.5bar kept spluttering didnt do nothing just stopped parked up then set off again

checked all pipes etc no signs of leaks, when was on motor way she was cruising at 100 without boost fine soon as i tried floor it abit wouldnt budge past 0.5

ran a fault code check no codes

turbo spools up normal no issues with that, cant get me head round it
any ideas