How can national or domestic law replace International law? A treaty between two sovereign entities is governed by International law and one entity changing domestic law has zero effect or applicability to the actual treaty. What we are changing is domestic law that gave effect to the treaty and in a way that is contrary to the treaty.
We are breaking international law. Rather helpfully the Govt has admitted to this in the House. Everything else thereafter is spin, obfuscation and lies.
More to the point by doing so we make every treaty or international agreement we have ‘non-binding’, and means any future treaty or international agreement is ‘non-binding’ as we now reserve the right to unilaterally change domestic law that gives them effect. This from a country that went to war on the back of a promise to another country.
We pride ourselves, perhaps somewhat romantically, that our word means something. It no longer does.