You could say this about any treaty, any agreement. And technically, a Sovereign Nation, by its very definition, is allowed to do whatever the fuck it wants. B

You could say this about any treaty, any agreement. And technically, a Sovereign Nation, by its very definition, is allowed to do whatever the fuck it wants. Before 20th century, breaches of treaties were grounds for war. Now we don't do that anymore, we simply cut off trade. So the U.K would be ostracized, International companies would move out, it would probably face high tariffs on goods (or outright ban) etc.