The real issue, surely, is that Johnson does not have the confidence of the Commons and should have quit when the Benn bill passed
Anne Twomey, who literally wrote the book on the prerogative, has written an important blog post that cuts through much of the legal machinations:
When is prorogation ‘improper’?https://t.co/GR7rMJ6Gkt
The answer: if the government is seeking to avoid a vote of no confidence
— Jack Simson Caird (@jasimsoncaird) September 19, 2019
The blog post above, which is well worth reading in full, from a leading academic expert on the prerogative articulates something which has not really been taken up before. The fact is that PMs derive their authority by being able to command a majority in the House of Commons. So far in his short premiership Johnson has lost every vote including one that could be regarded as issue of confidence – the Benn bill which is now law. Arguably Johnson should have quit when that bill went through against the wishes of his government.
Professor Anne Twomey states:
“Where prorogation is undertaken at the behest of a government which has, or appears likely to have, lost the confidence of the lower House, and is done for the purpose of avoiding a vote of no confidence or other action by Parliament against the government’s will (which may amount to an implied vote of no confidence), then such action may be regarded as ‘unconstitutional’ and may legitimately be rejected by the Queen”
This view could be important if the Supreme Court rules next week that the prorogation was null and void and Johnson, no doubt at the behest of Cummings,seeks to close Parliament down again. The Queen could refuse such a request.
All could have been different if in the immediate aftermath of Johnson’s victory in the Tory leadership contest there had been an effort to legitimise his premiership by winning a key vote in the Commons. I’d suggest that it would have been a lot easier then than it would now.