The government is the government, the Cabinet Manual says, ‘by virtue of its ability to command the confidence of the House of Commons’. The same principle applies to the prime minister. In ordinary political times, it is of interest mostly to pedants in arguments about ‘unelected’ prime ministers: they point out that no prime minister is directly elected, so to argue that, say, Gordon Brown (or John Major, or James Callaghan, or Harold Macmillan) improperly succeeded to the post without a general election is a category error.

For all their constitutional punctiliousness, the pedants miss the most provocative implication of popular grousing about ‘unelected’ PMs: that many voters understand their ballot to mean something other than a vote for an individual MP, and they cast it with parties and potential prime ministers in mind. Such mismatches between popular motivation and formal democratic structure are common, though British democracy has been historically adept at muffling popular discontent under parliamentary pomp and arcana. Hostility to prime ministers who enter Number 10 without popular sanction – part of what doomed Gordon Brown – ought to embolden Boris Johnson’s opponents.

Some of them, however, are looking to oust him by doubling down on the parliamentary arcana. One of the more outlandish ideas, advocated by the new Liberal Democrat leadership and taken up enthusiastically on the Guardian’s comment pages, is the imposition of a ‘government of national unity’ through improbable parliamentary insurrection. A temporary government headed by a backbench Labour MP (Margaret Beckett has been suggested as a possible leader of the junta), but supported by all who oppose Johnson, could seek an extension to Article 50 and impose a second referendum or general election.

Such a notion has been thrown up intermittently in recent years, usually with a Liberal at the head of the imaginary government. It is a perfect fantasy for a species of technocratic British liberalism: larded with patriotic nostalgia for wartime unity governments, smothering political conflict and ideological difference in a process-oriented parliamentary coup. One obvious objection is that it confirms to many Leavers their suspicion about politicians’ anti-democratic instincts, though it is also obvious that a portion of Leavers are now determined to view anything short of war with France as quisling treachery.

The fantasy is also only plausible to those driven as much by anti-Corbynism as opposition to Brexit: in fact, opposition to Corbyn is what requires its contortions in the first place. If anyone is going to try to form an alternative government out of the current House of Commons, it should be the leader of the second largest party (which got 40 per cent of the vote in the last election); the system accords certain privileges to Corbyn as leader of the opposition. To expect him to allow a Labour backbencher to be designated PM instead of him is a fundamentally unserious demand.

Interpretations of Boris Johnson’s Brexit strategy divide into two camps. The first understands him to have accepted that leaving without a deal is the only way for him to cohere the former Tory electoral base – now half decamped to Nigel Farage – into a single bloc; any expressed preference for a new deal is expedient but empty rhetoric. The second understands the emphasis on No Deal preparations as a means of provoking both Parliament and the EU, either into granting him last-minute concessions or ‘forcing’ him into an election. He would fight it as a tribune of Brexit, trammelled by a treacherous Parliament, seeking the latitude of a larger majority to remake the country.

Dominic Cummings, Johnson’s greatly overestimated aide, promises that however Parliament tries to constrain the prime minister, even by toppling the government, he will force through Brexit on the promised departure date. The hope is to turn Brexit into a runaway train, with Vote Leave cadres guarding any access to the driver’s cab.

For Johnson’s opponents, the problem is to find an emergency brake. MPs fear, not without reason, that they have less power than at first appears: the Commons has been difficult to corral into opposing No Deal, and Tory rebels have often proved suddenly invertebrate in the division lobby. Parliamentary time is thin, and Johnson’s government will try to forestall any opportunity for MPs to seize control of the order paper.

One backbench hope is to introduce a new version of the Cooper bill to rule out No Deal, looking to the speaker as an ally. John Bercow has suggested in the past that the standing order governing emergency debates might be interpreted by his office to allow for a substantive, amendable motion. Brexit fundamentalists would cry blue murder, and constitutional scholars would tut at the innovation, but Bercow insists that the rules exist to serve Parliament in the expression of its will rather than to hobble it. His support is no guarantee of easy passage through Parliament, however: any Tory voting for it will enrage both their whip and their base, and will find Nigel Farage’s sectaries targeting their constituency. The last bill mandating an extension scraped through by one vote at its third reading, only days from the deadline. Such an option may not be feasible until after the mid-October EU Commission meeting; even then, EU approval of a new extension without a referendum or election is far from guaranteed.

The other option is to collapse the government, through a confidence vote moved according to the Fixed-Term Parliaments Act. The uncertainties surrounding this are well known: whether there are enough Tory rebels; which way the various independent MPs would vote, knowing they’d be likely to lose their seats in any snap election; when (if at all) Johnson would resign were he to lose; how a replacement government would be formed, and by whom (John McDonnell has said he would put Jeremy Corbyn in a taxi to Buckingham Palace if a no confidence vote succeeded).

The major building blocks of an anti-Johnson vote in the Commons are sliding into place: there were reports at the weekend of an agreement between Labour and the SNP. The SNP has little affection for Corbyn, but its leadership will remember the electoral punishment meted out to them after they were seen to grease the rails for Thatcher’s entry to Downing Street in 1979. The Liberal Democrats are holding out, however, with Jo Swinson saying she won’t support Corbyn, and anonymous MPs rehearsing Conservative attack lines from 2017 in the national press. Swinson may have painted herself into a corner here, implicitly ruling out agreements with any party but the Conservatives: it is hard to see how she could refuse to support motions by a united Labour and SNP bloc. She could risk her seat by doing so – she lost East Dunbartonshire to the SNP between 2015 and 2017 as part of the post-coalition Liberal Democrat collapse – and her opposition to No Deal doesn’t look all that serious if she isn’t prepared to join forces with Corbyn, however briefly, to prevent it.

The final unknown squats behind the door of Number 10. Cummings and Johnson believe that everything can be reduced to a matter of intensity of commitment and powered by voluntaristic brio. It’s a mode suited to campaigning, where passion can hold together impossible tensions and antinomies, but toxic and self-defeating in the constructive work of rule. It also makes obvious the torsion between the two concepts of democracy at work in British politics. One considers democracy a singular event that happened in June 2016: the purpose of all politics is to implement and administer the referendum result, and under its sign all sorts of petty decisionism and amateur Caesarism can be countenanced. The second considers democracy an ongoing, piecemeal, iterative work, in which the future is shaped by new elections and debates as much as by the referendum. Across the House in the past few years, many have praised the flexibility and adaptability of Britain’s constitution: it may well soon be stretched to the point of rupture.