Thanks for that, Dave. Read and digest these remarks of Tony Grayling from that piece, Keith et al.:

First, earlier in your letter you say, 'The Government's position is clear that invoking Article 50 is a prerogative power…' We have seen that the Chief Justice and his colleagues in the Divisional Court do not agree with the Government on this, and we await the Supreme Court's view too. Should the justices of the Supreme Court concur, you have the delicate irony of a possibility: that of making a further appeal to the European Court of Justice. It will however be a matter of surprise if any panel of justices were to think that the UK Government has a prerogative power which would have enabled it to take the UK out of the EU even without a referendum, and whenever it wished; which is the clear – and absurd – implication of the Government's position.

...as to the larger sense of sovereignty you wish to imply, namely the sovereignty of the UK as a state: well! we are members of NATO, the WTO, the UN, we have obligations under international law, we have duties to allies; we have constraints as a result of treaties, trade deals, and internationally-binding contracts; and we exist in a tightly globalized world economy. In light of this the concept of the 'sovereignty' of any state is an empty piece of rhetoric. So talk of 'sovereignty' in this connection it is the kind of waffling cant used by politicians in elections and referendums which signifies little.

The government's position is that it has the prerogative to invoke Article 50. As the referendum was advisory and not legally-binding, the implication is that it wasn't actually necessary to hold one at all in order to gain that prerogative. The result is simply being taken by the government as non-legal support for that already-existing prerogative. An advisory referendum can't alone accord prerogative to the government. The government's position is that it can trump constitutional requirements. Well I think we need to remind them that we are still a democracy. The second bit I quoted is a solid argument for saying that all the "taking back control" talk by the brexit side was just another pack of lies. "Sovereignty" as a concept for the nation is in disrepute as a consequence of the term's serial misuse by little Englanders. We should make sure that the Tories are not allowed to bring the word into disrepute with regard to parliament.