Unless this has been deferred/revoked, a diesel car which was originally equipped with a cat that has subsequently been removed will fail. That's according to a notice to testers something like 02/14.... does anybody know different?
Of course tester has to know your car was cat equipped and be able to see its not now...
As far as I am aware, with the rules that came that date you mentioned, all cars, petrol or diesel that had cats and/or dpfs fitted when first built, must still have them on, whether it be original spec or sports version.
Saying that, mine still has the decat pipe on and passed all its MOTs, so far (touch wood ).
But, when I take it to the garage for service and MOT I am still taking the cat and leaving it with the garage just in case the independant tester they take it to fails the car, that way they can refit and take back the same day.