Does a de-cat affect MOT emissions?

[mrvillicus]

Last week my car developed a really loud metallic rattle coming from the exhaust. I fitted an aftermarket brand new cat last June so I thought "it can't be that", it must be the old and rusty centre box. So today I had a Bosal centre box fitted for £80 and guess what...the rattles still there. It's a lot worse when I'm reversing at low revs strangely and it is very noticeable at tickover and in 4th or 5th gear when driving so before I investigate tomorrow I'm thinking it must be the flexi pipe in the cat which brings me to my question...if I fit a de-cat pipe will it affect my emissions when its MOT time? I know people are going to tell me that it was designed with a cat and that cat's save the planet which I completely agree with however I cant afford an OEM cat, and it seems these aftermarket CATs are a waste of time

Ben