A point I would make is that most of these supposedly British ships are: (a) not built in Britain (b) owned ultimately by foreigners (c) captained by foreigners (d) crewed by foreigners (e) shipping foreign goods (oil) (f) from foreign ports (g) to foreign ports. Not complaining about foreigners, my point being that these ships are not very British at all. But one of the companies in a complicated chain is nominally British, the ship is listed on a UK register, and a British flag is flown; and UK statisticians can pretend that such shipping is part of the UK's GNP hence claiming fifth position in the GNP boasting stakes. We the (UK) would be better off out of this game. Let their owners register them with Panama and see if Panama will declare war on Iran. Some owners are re-registering with France, who have a navy and lack a quarrel with Iran.