Potential fine of up to £2500 ,
your most likely to get a vehicle defect notice , but remember that up to £2500 if they want to take you to court and make an example of you in conjunction with something else .
if declared to your insurer you have no real issue on the insurance side , however you must have stated a decat and that they are happy with that knowing it falls foul of emission regs on most newer cars .
decat pipes are fine to use on older cars before the regs changed , for example a 93 1.9 gti pug has a cat and taking it off won't fail the emission test , certain porsches have had cats since the early 80's so there are cars that can use a decat quiet legally on the road ....
apart from making the car noisier , the benefits on a non turbo car are tiny ,so why run the risk ??