The inspector may call any person present at the place where the inquiry is conducted to appear before, him, irrespective of whether or not such person was summoned under regulation 11.2.2, and may -
(a) examine such person or cause such person to be examined by any other person;
(b) require such person to produce a book, document or thing specified in the summons or which he may have with him;
(c) retain for a reasonable period any book, document or thing produced by such person or seize it if in his opinion it may serve as evidence at the trail of any person charged with any offence under the Act, these regulations or the common law.