When Australia sneezes, the world catches a cold. So be warned that they had an unusually early and quite nasty flu season down under this year. I mention this because fear of the flu is one of the hidden reasons why Boris Johnson craves a pre-Christmas election.

Senior NHS officials have warned ministers that the severe flu season in Australia is likely to be a harbinger of the same here. That will compound what already threatens to be a grim winter for a stretched health service. Better, then, from a Conservative perspective, to have an election in the first half of December rather than wait until January or February when news bulletins may be nightly leading with reports of a winter crisis putting more pressure on intensive care and high-dependency units than the NHS can cope with. The thing most worrying to ministers is a repeat of the winter of 2017-18 when a bad flu season in Australia was followed by a killer one in Britain, which saw deaths hit a 42-year peak after the flu jab failed to work in the majority of cases.

Because a winter crisis in the NHS would be menacing to the Tories’ electoral prospects it would be conversely advantageous for Labour. They would be armed with ammunition for their argument that the Conservatives have run down key public services. Labour people also think they would be able to move the national conversation off Brexit and on to a topic where the party is much more comfortable. The salience of the NHS as an issue with the voters typically rockets after Christmas, whether or not there is a flu epidemic. Labour people won’t say this in public unless they are complete idiots, but I know that the prospect of a winter NHS crisis has featured in shadow cabinet debates about whether to agree to a pre-Christmas election.

Politicians are often at their most dishonest when it comes to election timing and neither party is being straight about their reasons for wanting or not wanting to fight a campaign held to a festive soundtrack of perfume ads and gritting lorries.

‘Jeremy Corbyn has not disciplined any of the 19 Labour MPs who helped the Tory leader to that victory by joining him in the aye lobby for the bill’s second reading.’ Photograph: Andrew Milligan/PA

Begin with Boris Johnson. He’s already made two thwarted bids to trigger an election and plans another after MPs stymied his attempt to ram the Brexit legislation through parliament in a breakneck three days. He claims he needs an election because an obstructive parliament is standing in the way of his mission to “get Brexit done”. Yet the means to get on with doing it are in his own hands. He can simply unpause the withdrawal legislation. It was approved in principle by a majority of 30, a chunky margin in the current circumstances. It is notable that Jeremy Corbyn has not disciplined any of the 19 Labour MPs who helped the Tory leader to that victory by joining him in the aye lobby for the bill’s second reading. One of Labour’s frontbench, Jo Platt, voted with the Tories and she hasn’t been sacked from her job, which would be the usual sanction against a member of the shadow team who defied the party whip. This is better than a nod and a wink to the pro-Brexit contingent of Labour MPs that Mr Corbyn would think himself suited if the legislation proceeded through parliament.

If the government offered a more reasonable timetable for scrutiny of the withdrawal agreement, it would almost certainly be agreed to. It would also be extremely likely that the European Union would offer a sufficiently ample extension for that to happen. Of course – and this is an important reason why he wants a quick election – the Johnson deal could start to fall apart once it is subject to detailed examination and the coalition that won him the second reading vote might unravel. If parliament wrecked the legislation further down the track, he could always return to his demand for an election – with more force.

He wants a swift election because his chief strategist, Dominic Cummings, calculates that this is the way to maximise the chance of victory by framing it as the “people versus parliament” contest that he has been preparing for from the moment he moved in to Number 10. Not all Tories think this a sensible strategy. Some believe, and this includes a fair number of the cabinet, that they’d have a more powerful pitch if they held off until next year and went to the country after Brexit had been “done”. In truth, it would not be “done” at all, but they would present it as such and hope to bank an electoral reward. Other Tories are anxious about the corrosive consequences for trust in our democratic institutions of waging a “people versus parliament” election. A winter election is unpopular with some Conservative MPs for other reasons. Their Scottish contingent, already an endangered species, don’t fancy the thought of canvassing on dark streets in hostile weather. Tories who will be defending Remain-leaning seats against Lib Dem challengers will be made more vulnerable in a campaign that polarises on Remain/Leave lines. But the Cummings battle plan regards them as sacrificeable. The road to a Conservative majority that he envisages does not run through Scotland or even Surrey, but through taking seats off Labour in the north of England, the Midlands and Wales.

‘Jennie Formby, the party’s general secretary, was asked how many constituencies still hadn’t selected a candidate and which ones were on the key seat list. I’m told that she couldn’t answer either question.’ Photograph: Michael Mayhew/Sportsphoto Ltd./Allstar

In the old days, Mr Johnson would have got an election by simply dropping in on the Queen and asking for one. Thanks to the Fixed-term Parliaments Act, it is very hard for him to engineer a contest without the cooperation of the opposition. Labour is a mess of splits on the question. There are some hardcore Corbynites who seem genuinely keen on an election and sincerely convinced that the opinion polls are all wrong when they report that the party is dismally unpopular and its leader even more voter-repellent. His residual devotees cling to the faith that the miraculous gifts of Saint Jeremy will stun everyone by leading the party to triumph. When the shadow cabinet met on Tuesday, Laura Pidcock, the shadow minister for employment rights, launched into a little speech in which she declared: “Let’s sweep these establishment Tories from power with an insurgent Labour party!” Once Ms Pidcock had expended herself, Barbara Keeley, the shadow minister for mental health, drily responded: “I don’t see much insurgency in Salford.”

At an informal meeting of some of the shadow cabinet on Thursday, two of the strongest voices against allowing an election were John McDonnell, the shadow chancellor, and Nick Brown, the chief whip. Both have been bombarded by election-averse Labour MPs telling them that not only should there not be one, but that there will be a massive rebellion if the party leadership tries to whip Labour MPs to facilitate a pre-Christmas contest. “Do I fancy shivering on doorsteps in December trying to explain our Brexit policy?” says one Labour MP. “What do you think?” Another reports: “Various WhatsApp groups of Labour MPs are going wild with people telling colleagues that they won’t vote for an election.”

The obvious explanation is that turkeys don’t vote for Christmas, especially when the turkeys can read opinion polls suggesting that they will be stuffed. Members of Labour’s parliamentary committee, senior MPs who act as sort of shop stewards for their colleagues, were alarmed when they had a meeting last week with Jennie Formby, the party’s general secretary. She was asked how many constituencies still hadn’t selected a candidate and which ones were on the key seat list. I’m told that the general secretary couldn’t answer either of these election-critical questions.

Many of the senior officials responsible for Labour’s effort during the 2017 campaign have been purged from party headquarters or paid off. I hear that some are now being sounded out about coming back, such are the fears that Labour is not in a fit state to fight a campaign.

Mr Corbyn’s instinctive reflexes have previously been to go for it. He’s repeatedly called for an election and he’s finding it an increasing struggle to muster plausible excuses for why Labour won’t agree to one now. A proud man and a stubborn one, he doesn’t like looking scared of a contest and his remaining fans are telling him that he is a brilliant campaigner who will turn things around as he did in 2017. But colleagues who have spoken to the Labour leader very recently have come away concluding that he is “genuinely procrastinating”.

It is rarely an appealing look for a party to be frightened of an election and Labour could pay a penalty when it ultimately has to face the voters. To the majority of Labour MPs, that risk is outweighed by the perils of a pre-Christmas contest. Better, they think, to run scared than to get run over.

• Andrew Rawnsley is Chief Political Commentator of the Observer