3. The Merchant Shipping (Closing of Openings in Enclosed Superstructures and in Bulkheads above the Bulkhead Deck) Regulations 1988 (“the principal Regulations”) (which apply only to United Kingdom ro/ro passenger ships) shall, subject to regulations 4 and 5 of these Regulations, apply also to ro/ro passenger ships other than United Kingdom ships, while they are within a port in the United Kingdom.