Any person who is convicted of an offence against section thirteenF1 of the principal Act (which relates to summary proceedings against brothel keepers, &c.) shall be liable on summary conviction—
(a)to a fine not exceeding one hundred pounds or to imprisonment. …F2 for a term not exceeding three months; and
(b)on a second or subsequent conviction, to a fine not exceeding two hundred and fifty pounds or to imprisonment. …F2 for a term not exceeding six months;
or, in any such case, to both fine and imprisonment.