http://www.longlife.co.uk/blog/index.php/2012/04/removing-catalytic-converters-from-a-diesel-car-what-you-need-to-know/

Really useful, I was fairly sure it was the case despite previous posts claiming it wasn't. As a former range Rover (petrol) and Discovery owner (Diesel) I noticed it was common practice to remove the cats from the diesel versions of these vehicles along with the EGR valve. On my Disco i disconnected the EGR valve and I could certainly feel a difference. The engine seemed more responsive. Fuel consumption didn't improve as I as I think I used the new found responsiveness.

 

My superb is only 8 months old so I won't consider it - I wonder what the ECU etc. would do if such mods were carried out - and how much difference it would make to the car.

Cat and EGR removal on a diesel is ok without ECU modification. DPF removal would require a remap.

Never had any problems with a fast pass on my 05 Defender. It pays to have engine warmed up before the test to guarantee a fast pass though.

I wonder if the bhp would increase with the cat and DPF removed,

having one of the last 1.9s made, I think mine has just a cat