Corrosion that is either in a prescribed area, i.e. Seat Belt Mountings, Brake System Mounting Points, Steering Mounting Points or as part of the Body Structure will need to be repaired by Welding.
In the case of Body Sills it is often better to replace the sill than to repair it with a patch which, although a satisfactory repair for MOT purposes, will not prolong the life of the vehicle. Sill replacement is usually the best method of repair in this case.