It point blank cannot pass an MOT with no CAT.
there's no struggle about it. If it's not fitted it's a fail.
It'll be more drone with no cat fitted, you'll also have a slight reduction in back pressure. this will make the car less torquey mid range. If you're not mapping the car, it won't be running optimum.
Personally, I wouldn't fit the decat pipe if you're using it every day.
If it's a track toy, then go for it.