Not sure this is the case - the new rules that came in Feb 1st this year specifically relate to DPF filters (i.e. if they were fitted as standard, must be present for the test). A missing CAT is only a reason for failure if the car would be subject to a CAT emissions test (i.e. petrol after '92). From the MOT testers manual, there are 5 potential reasons for exhausts to fail the MOT:
1. An exhaust system not adequately supported.
2. A major leak of exhaust gases from any part of the system.
3. A catalytic converter missing where one was fitted as standard
4. A silencer in such condition, or of such a type, that the noise emitted from the vehicle is clearly unreasonably above the level expected from a similar vehicle with a standard silencer in average condition.
5. An exhaust tailpipe positioned so that fumes are likely to enter the drivers or passenger area.
