Originally Posted by RichieST

I wouldn't advise supermarket fuel, although it all comes from the same refinery, branded fuels have additives in them which the supermarket fuels do not have. I've always got better MPG and smoother running using branded fuels than supermarket.

Definately try removing the EGR valve and cleaning it as it will be a lot more effective than a can of additive for the fuel tank. You can get blanking plates off of ebay to remove the problem all together, maybe try one of these.