§ 9. "That during a period of five years beginning on the twenty-eighth day of April, nineteen hundred and twenty-eight, there shall be charged on the importation into Great Britain or Northern Ireland of buttons made of any material, and whether finished or unfinished, of a description commonly used for the fastening o decorating of wearing apparel or household linen, not being buttons forming part of any other article, a duty of customs of an amount equal to thirty-three and one-third per cent. of the value thereof."