At this event in Feb, I asked Jonathan Jones, who has reportedly just resigned over the government's threats to breach the withdrawal agreement, what approach gvt takes to international law. His answer is.... illuminating.
1/ https://www.instituteforgovernment.org.uk/events/legal-advice-government-conversation-treasury-solicitor

I asked: What approach do gvt lawyers take to these obligations given that, unlike domestic rules, they are not enforceable against the government before the UK courts? He said: "Fundamentally, international law is the law. It derives from obligations the government has...
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entered into through treaty or otherwise arise under international law. We treat that as the law, and the government is subject to the rule of law and will comply with those obligations. So, the role of the lawyer [...] will be just the same: to give the best, professional...
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advice as to what the law means, how it applies, and so what is the risk that a given course of conduct may be incompatible with that law."

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