Any test of goods purchased under paragraph 1(1) or seized under paragraph 4 by or on behalf of an enforcement authority for the purposes of ascertaining whether the provisions of these Regulations have been contravened must in all cases be carried out in accordance with the provisions of paragraphs 2 to 5 of Schedule 3 and any test for which a method is specified in paragraph 6 of Schedule 3 must be carried out in accordance with that method.