4At any contested election of four or more members of the Senate of Southern Ireland or of Northern Ireland, the election shall be according to the principle of proportional representation, each elector having one transferable vote as defined by the Representation of the People Act, 1918, and His Majesty in Council shall have the same power of making regulations in respect thereto as he has under subsection (3) of section twenty of that Act and that subsection shall apply accordingly.