s 73 Disapplication of rules to mandatory terms and notices
(1) This Part does not apply to a term of a contract, or to a notice, to the extent that it reflects— (a) mandatory statutory or regulatory provisions, or (b) the provisions or principles of an international convention to which the United Kingdom ... is a party. (2) In subsection (1) “ mandatory statutory or regulatory provisions ” includes rules which, according to law, apply between the parties on the basis that no other arrangements have been established.