Strikes me as a horrible (and cynical) misinterpretation of that decision. There's no dispute that Parliament, and only Parliament, can pass whatever domestic laws it likes, but to do so is consistent only in domestic law, and not in international law. If the UK breaches its international obligations -- and, let's be clear, the Government is
admitting that its proposed legislation does this -- then it would be in breach of international law and can expect to face the consequences of doing so.
I'm no expert in Constitutional Law, so I'm going to cite the argument below, from someone who *is*:
https://twitter.com/ProfMarkElliott/status/1304076133827309569
I'd also add that the point of International Law is that it's trying to treat all sovereign nations as equally sovereign. It stands to reason that, if two sovereign nations or groups of nations reach an agreement, then for one of them to unilaterally break that agreement is to disrespect the sovereignty of the other. This is why we condemn nations like Russia, Iran, China, North Korea, etc, etc, etc, for being so often in flagrant violation of International Law. Deliberately breaking it in this case is just cynical and wrong, and I seriously hope that it's just a misguided attempt at a bargaining chip.