If they don't want to follow a treaty they should rescind it. Until then it is the law of the land and it should be followed.
Or not, as parliament is free to decide. I think my previous statement on parliamentary supremacy stands for itself. If you have something specific to talk about from that Wikipedia page, it's best that you spell it out for us.
Stuff like this may have a certain level of "might makes right" (similar question for Hawaii, although there it's obvious who would win in a fight) but not always (Irish independence at close to the peak of the British Empire, the Cod Wars, that the US didn't keep all of Mexico after the war, just Texas, Arizona, California, etc.)
Of course they have a casus belli. They’d lose if there was a war though so there’s that.