He's talking absolute rubbish.
The law states that firms with more than 250 employees MUST charge for carrier bags. As long as the bags are within the size/thickness limits defined in the legislation, there can be NO exceptions (other than those exceptions allowed by law anyway, such as when the bags are used solely to wrap certain loose or wet products).
(BTW: The rule about 250 employees is applied in England. It may be different elsewhere; in Wales for example, ALL shops must charge for carrier bags)