Thanks for all your replies! I use our leak tester on the dpf pressure pipe and have already used it on the intake side and found no leaks. The pressure reading drops back to minus 1kpa at idle now after i took the dpf off yesterday and cleaned it out. I took the car on a 20 mile road test and it now flies with no error reported.
Seems to be fine now but the minus kpa is worrying me slightly??