http://www.legislation.gov.uk/id/uksi/1987/37

SCHEDULE 4FLAG INDICATING THAT A VESSEL IS CARRYING A DANGEROUS SUBSTANCE

PART IImaterial and size of flag on vessels with a mast

2.

The side of the flag marked “a” on the diagram shown in Part I of this Schedule shall be not less than 75 centimetres in length and the sides of the flag marked “b” on the said diagram shall have equal lengths of not less than 90 centimetres.