You can NOT fit drop plates to Type Approved towbars as this will invalidate the Type Approval unless the towbar was tested with one.
A. All Tow-Trust Type Approved Towbars carry a label which provides information such as;
A. If your passenger vehicle was first registered on or after 1st August 1998 you must fit a Type Approved towbar. Failing to do so may lead to your prosecution or your insurer failing to pay out should the vehicle be involved in an accident.