Unfortunately the legislation changed in February and now any diesel of any year will fail the MOT if it was fitted as standard with a CAT and/or DPF filter in the exhaust system which has subsequently been removed. It's a difficult and frustrating area as it means that a car which is perfectly safe to drive on the roads will now fail the test when last year it passed. So far as I am aware, there is also no official way of the tester finding out if the car did have one as standard - for example some 1996-ish 300 TDI Disco's had them, some did not. Hence it is inevitable that some cars will be failed in error.
A point to bear in mind though - there is currently no specific test of the function of either the CAT or DPF filter (unlike on Petrol cars) - the test is limited to the presence of one. So you could get a second hand one on e-bay, knock the guts out of it and then fit that. Not good news though for people who have bought full exhaust systems.
It's an interesting topic as not all MOT testers are rigidly enforcing the new rules - many are frustrated that the test has gone way beyond a road worthiness check. They are supposed to fail cars for trivial reasons now which affects their relationship with long standing customers.
