4.The Secretary of State may by order provide that, in relation to a carrier whose principal place of business is in the United Kingdom, paragraph 1 of article 7 shall have effect with the substitution for the limit for the time being specified in that paragraph of a different limit specified in the order (which shall not be lower than the limit specified in that paragraph at the passing of this Act or, if paragraph 1 of Part III of this Schedule has come into force, specified in paragraph 1 of article 7 as amended by paragraph 1 of that Part).