Whenever in connection with any area in respect of which two or more training boards have been accredited in respect of different industries, there is in the opinion of the Minister doubt as to whether any operation falls within the scope of a designated trade in an industry in respect of which one of those training boards has been accredited, or within the scope of a designated trade in an industry in respect of which any other of those training boards has been accredited, the Minister shall, after consultation with the board and the training boards in question, determine the matter, and the Minister may in the same manner vary any such determination.