Cat ist required on a diesel for an MOT.

As long as it passes the opacity test its all gravy.
 
Hmmm thats closer to what I was told....

My tuning box should be okay shouldnt it... ie it only adjusts fuel to the top half of the system etc etc....

i would take thr TB off if i were you. from my experience when i had mine i took it off 5 mins before its first MOT, went for a quick blast to try and clear it out a bit then put it in for the MOT, they had trouble getting it through, had to put some injector cleaner in and do more blasts around the block to get it to pass and then only just.

thats just my experience. i never did another MOT with it as i sold it after that.
 
what are the advantages of not having a cat?

better performance?

and i guess minus the cost of a cat?