A removable auxiliary seat fitting behind the rear seats of an estate car has a backrest 14 extending across the car behind the backrest 11 of the rear seats, and a squab 13 resting on the floor. The backrest 14 is secured by brackets 25 attached by the bolts for the mechanism for locking the backrest 11 in its upright position. The auxiliary seat assembly may have seat belts mounted on the same bolts as those used for the existing rear seat belts.