just re-read this and realised you are actually asking if the car has to have a spare wheel
WELLno it doesn't nothing to do with the MOT test. However if you do plate it over, you should really seam weld it as it'll class as a "repair" within a certain distance of a major suspension pickup point.
Although you can get around it by fixing it strongly and applying a lot of underseal! They'll not be able to tell if it's seam welded or not