Delays. The threat of sudden cancellation. Expensive. The story of HS2 is that of the modern rail traveller writ large. Now a decision on whether the £100bn-plus project should go ahead is imminent.

The are no certainties in politics but despite the misgivings of Boris Johnson and his senior Downing Street advisers it looks as if the green signal will be given for the line connecting London with Manchester and Leeds.

Channelling his inner Oscar Wilde, the prime minister seems to have concluded that the only thing worse than going ahead with HS2 is not going ahead with it. The official government report into the project rejects the idea that canning HS2 would lead to a flurry of alternative rail local improvements in the north of England. Instead, it says there would be an infrastructure drought at a time when the abysmal quality of service has forced ministers to renationalise Northern rail.

The politics of this are obvious. It would be a slap in the face to all those new northern Conservative voters if Johnson pulled the plug on HS2 and had nothing to replace it with. It would make a nonsense of his avowed intention to rebalance Britain’s regions.

But the prime minister’s lack of enthusiasm for HS2 is palpable. Giving it the go-ahead looks like a bit of a personal setback. So how does he turn defeat into victory?

One way would be to combine final approval for HS2 with an announcement that the third runway at Heathrow will no longer go ahead. Business – which is keen on an expansion of London’s biggest airport – is waking up to this possibility.

“I am worried about the third runway at Heathrow,” one business leader said recently. “It hasn’t passed all its legal hurdles and everything has gone quiet. Anything could happen.”

From a Downing Street perspective, saying no to Heathrow expansion ticks a lot of boxes. For a start, the prime minister is a lot more hostile to a third runway than he is to HS2. When he was elected to parliament in 2015 he vowed to lie down in front of the bulldozers to prevent the project going ahead. When the issue came before parliament in 2018, the then foreign secretary was so embarrassed that he made sure he was out of the country and did not have to vote. It would do the prime minister no harm at all to be seen – for once – to be keeping his promises.

Johnson’s seat of Uxbridge and South Ruislip will be affected by Heathrow expansion, but so will a lot of other constituencies in west London. There were not that many Conservative losses in the 2019 general election but two of them were in seats under the Heathrow flight path: Putney and Richmond Park. Brexit was the key issue in these heavily remain-voting seats, but the support given by Theresa May’s government to a third runway will certainly not have helped.

The cost of a third runway at Heathrow is put at £14bn – a fraction of the current budget for HS2 – and the money is supposed to come from the private sector. But there have already been questions asked about the ability of Heathrow’s owners to find the cash necessary for the investment, leaving open the possibility that passengers and taxpayers will end up picking up a large chunk of the bill. In any event, the Treasury will have to stump up for the improved road and rail infrastructure that will be needed.

Saying no to Heathrow would also counter one of the criticisms levied by Labour councils in the north: that London and the south-east gets more than their fair share of public infrastructure spending. Sajid Javid is expected to announce new rules in his March budget that will lead to investment decisions being less focused on national economic growth and more on the impact it will have on helping poorer parts of the country. A tough approach to a third runway would help convince sceptics that the government means it when it says it intends to level up Britain.

Last but not least, abandoning plans for a third Heathrow would burnish the government’s green credentials in the run-up to the crucial climate change summit being held in Glasgow later this year.

Ministers are desperate for COP26 to be a success but know that it will be judged a failure unless they can get international support for speedier action to reduce carbon emissions. One way of doing that would be for the UK to take the lead by noting an inconsistency between planning for a net zero carbon economy on the one hand and encouraging air travel on the other.

There are, of course, other factors for the government to consider. It is keen for Britain to be seen as an outward looking country after Brexit and international connectivity is part of the narrative. Business groups will kick up a stink, arguing there will be a loss to jobs and competitiveness, and that passengers will decamp from London to places such as Amsterdam and Frankfurt, where there is more capacity. Carbon emissions will go down in Britain, but go up elsewhere.

Still, the prime minister likes a big announcement and a grand bargain that involved yes to HS2 and no to Heathrow would fall into that category. Business is right: it has all gone very quiet on the question of a third runway. By no stretch of the imagination does Whitehall’s silence definitely mean that Downing Street is cooking something up, and there has been no briefing to that effect. But if Johnson is not rethinking government policy towards Heathrow expansion, then he ought to be.