From ADR book thingo btw im typing this and had a few beers so i cbf looking at my spelling, here goes.
SEAT BELTS
The level of safety provided by seat belts muct not be reduced. Seat belts must not be replaced by belts of a lesser standard or with seccond hand belts, eg, lap belts must not be used in place of lap/sash seat belts. The use of retractable seat belt disabling device is not acceptable.
and another section saiz.
seat belts must be installed for all seating postition. lap/sash seatbelts are required for all dont and rear outboard seating postitions. lap/sash or lap belts shall be fitted to imboard seating positions.
theres other things on it but essentially what their saying is it has to retract. this may be for reasons of safety in emergency situations.
eg u drifto into a pole and doors are jamed shut cause u bent your chassis, and your no2 tank is leaking causing you to go unconcous, your engine is reving to 9k with the turbo blowing the ceramic housing out your cat and, the guy that lives in the trailer park is running to save your ass, cant work out how to undo your funny looking fulli sik drifto seatbelt.
or u can have it legal and stock and live.