De-cat, MOT and Fuel Economy

When I was getting my MOT done on Monday (after spending the weekend welding) I asked the man about de-catting my 300TDi. He confirmed what most people say on here, that he doesn't care whether or not there is a cat fitted as long as it passes the emissions test. However, he also said that removing the cat would cause the fuel consumption to go up....any one know how he worked that out?

I'm not quite sure how he arrived at that conclusion to be honest. You'd have a mild case in some cars that if you removed the cat you would lose a little back pressure, which some engines need, but on a turbocharged engine the back pressure is right on the manifold, because it's the turbo.

Might have meant that you'd be more inclined to drive it harder?

ive de-catted mine and de-egr d getting better fuel economy me thinks maybe you should take your landy somewhere else

Yes I was thinking if anything I should get better fuel economy with the cat removed. I only let these people MOT it cos they are close to where I work...they haven't done anything else.