The Betting, Gaming and Lotteries Act 1963 shall have effect as if in paragraph 3(a) of Schedule 5, after the words “six per cent” there were inserted the words “or such other percentage as may be specified in an order made by the Secretary of State by statutory instrument” and as if at the end of paragraph 3 of that Schedule there were inserted the following— “ Any power conferred by this paragraph to make an order shall include power to vary or revoke the order by subsequent order. ”