I thought about removing the CAT on mine so asked a friend in the know, he said it's not a CAT as such but a DPF (Diesel Particulate Filter) only on the newer generation of diesels does the DPF also act as a CAT (ie, removes or converts gasses), the older type is basicly just a filter so removing it may increase the particulate count and cause the vehicle to fail the mot, it would also give you a pretty much straight through exhast system, good for performance but noisier.
I had a quick look on google and this does seem to be the case.
I suppose it depends on how much soot your engine is chucking out in the first place ?