rear seats legality?

my disco bobtail has the rear seats removed and a chequer plate floor and square arches welded in so the original seats cant be refitted
so im gonna fit a pair of bucket seats

regarding seat belts and the mot can I fit harnesses that are integral to the seat or do harnesses or seat belts both have to be secured indipendantly to the floor?

it can be part of the seat, but the seat fixings are beefed up to take the load of the belt, mini buses have this setup,

belts on seat = seat fixings to chassis