(1) A power conferred by virtue of this Act on a constable -
(a) is additional to powers which he has at common law or by virtue of any other enactment, and
(b) shall not be taken to affect those powers.
(2) A constable may if necessary use reasonable force for the purpose of exercising a power conferred on him by virtue of this Act (apart from paragraphs 2 and 3 of Schedule 7).
(3) Where anything is seized by a constable under a power conferred by virtue of this Act, it may (unless the contrary intention appears) be retained for so long as is necessary in all the circumstances.