It is my understanding that removing the catalytic converter from any vehicle manufactured from 1993 onwards is illegal. It contravenes the construction and use regulations, which state that all vehicles manufactured in 1993 and onwards HAVE to be fitted with a catalytic converter. All vehicles manufactured after that date must have the exhaust gasses passed through a converter. It is even an offence to fit a none type approved cat to a vehicle. It is also a technical MOT failure, in that the exhaust is incomplete or has parts missing or has been retro fitted with a none type approved cat, reference the certificate of construction and use compliance and type certification issued to the manufactures.
Not a lot of people know that.