India, Sept. 21 -- Which is sovereign, the people or Parliament? Is the Crown - that is the Government - entitled to interpret the wishes of the former and override the latter? Should the courts intervene in these arguments, something they have been reluctant to do since 1689? Such arcane questions, once the dusty preserve of academic jurists, are now central to politics in Britain. The bedrock of the UK's Constitutional settlement, the separation of powers, has been shaken to its foundations by Brexit .

There have been so many unprecedented political events since the referendum in 2016 that is easy to be blase about the proceedings taking place in the Supreme Court. And yet this is arguably the most extraordinary moment of them all. Her...