The more things change he more they stay the same...SOLAS Regulations. The United Kingdom is signatory of and has ratified the International Convention for the Safety of Life at Sea 1974
Because Parliament has ratified the Treaty it becomes part of UK municipal (ie domestic) law. As Photex says, it is not discretionary. To not follow some aspects of it that you don't like would be the same as choosing not to apply aspects of IHL (or LOAC, as the Army prefers to call it).
Slavery advocates argued that nothing could be done due to contract law.