The current combination of Brexit bluster from No 10 and Corbynista claims seem to have confused even the shrewder media commentators: the rest are swallowing spin from both sides without any attempt at fact checking.
The idea that the Leader of the Official Opposition has a constitutional right to form an alternative government as soon as the current Prime Minister is defeated by a Vote of Confidence is wishful thinking by the Corbyn coterie. Similarly, the notion that Johnson can simply trigger a General Election in such circumstances is against the law.
Let me take you back to the Fixed Term Parliaments Act (which I argued for even before the 2010 election resulted in the failure of either of their parties to achieve a Commons majority). There was no logic to the previous convention. Nor could it be claimed to be fair. The captain of one political team could simply blow the final whistle whenever he/she judged that they had the best chance of winning.
In a parliamentary democracy we Liberal Democrats argued – successfully – that was a totally unacceptable anomaly, more suited to an “elective dictatorship”, as described by erstwhile Tory Chancellor Lord Hailsham. Hence the 2011 Act, promoted by the Coalition Government.
Under the Act each Parliament will normally continue for a full five year period. An “Early Parliamentary General Election” can only happen in one of two circumstances. EITHER the Commons votes by a 2/3 majority (including vacant seats) for a specific motion calling for it (as happened in 2017), OR a Motion of No Confidence is passed against the current Government, and – after a 14 day interval – neither it, nor any alternative administration, has secured a Confidence Motion.
During that period the current PM cannot trigger an election: clause 3(2) reads “Parliament cannot otherwise be dissolved”. In that respect at least Dominic Cumming’s threats are absurd
However, as you will readily observe, it is one thing to prevent crash out Brexiteers from cutting MPs out of this particular nefarious sharp practice, but quite another to so manage the process to achieve a more democratic outcome.