Details of these regulations can be found in MGN 659 (M+F) amendment 1 entry into enclosed spaces.

https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/1066796/enclosed-spaces-guidance-for-merchant-vessel-operators.pdf

https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/1072817/MGN_659__M+F__Amendment_1_merchant_shipping_and_fishing_vessels__entry_into_enclosed_spaces__regulations_2022.pdf