The Oil in Navigable Waters (Heavy Diesel Oil) Regulations 1956
Regulation 2 applies to all British ships registered in the United Kingdom and permits, in certain circumstances, the discharge from bilges into a prohibited sea area of a mixture containing oil of particular descriptions.

Regulation 3 applies to British ships being tankers registered in the United Kingdom and permits, subject to prescribed conditions and in prescribed circumstances the discharge of oil-contaminated ballast or tank cleaning water into a prohibited sea area.

Regulation 4 app...