Prepare for the next instalment of the great HS2 fiasco. Stories suggest the chancellor is preparing to shuffle the off-balance sheet financing deck, find £1bn-plus and give a thumbs up to start boring the tunnel from Old Oak Common to Euston. That decision will be motivated mainly by the sense that the high-speed line, already stripped of its northern legs by Rishi Sunak, would be even more of a national embarrassment if southbound passengers had to hop off at an industrial estate five miles west of central London.

But, if the tunnel is a go, we’re on to the far trickier question of what is to be done with Euston station. Sunak’s other HS2 gift a year ago was to leave a sketch of an idea that few thought would fly. Developers would be recruited to build a stripped-down HS2 terminus. They would “unleash” private-sector money to build offices, shops and houses at the site “to ensure we get the best possible value for the British taxpayer”. Sunak’s “Network North” document from October 2023 made comparisons with the redevelopments of Battersea power station and Nine Elms.

The problem with that line of wishful thinking is that there isn’t a queue of would-be developers itching to risk their shirts at Euston. “The development is just too difficult and complex and the politics are too demanding,” says one leading industry executive. “And the site is just a big slab of concrete over the station with little room to expand northwards.” Meanwhile Lendlease, the Australian firm that is the lead developer, has announced plans to exit the UK.

One could understand Sunak’s loose reasoning, of course. Like HS2 itself, Euston seems to defy every attempt to impose control on costs. Two designs have already been ripped up. The last version came out at £4.8bn when the brief was £2.6bn. A scathing report from the public accounts committee in July last year said the Department for Transport still did not know what it was trying to achieve.

Well, quite. HS2 Ltd’s original design said 11 platforms, the next said 10 and Sunak wanted to go to six and remove the tunnel between Euston and Euston Square underground stations that had previously been seen as critical to dispersing HS2 passengers. Does the new government have a better idea? What is its view of the right number of platforms?

As railway folk always point out, the problem with six is that you curtail capacity for HS2 permanently. That model would, in effect, kill any distant hope of reviving building HS2 north of Birmingham. And the problem with the 10 or 11 is pure expense. The government could adopt a mayoral development corporation structure to try to inject more mission-like focus but, ultimately, everything points to a big slug of public money to underwrite the project.

It is hard to avoid the conclusion that Euston was always the wrong terminus for HS2. It is crowded already and doesn’t have the same connections, including Eurostar, as Kings Cross St Pancras half a mile up the road. Back in the days of peak optimism about HS2, Euston seems to have got the nod partly on the basis that a north-south Crossrail 2 would eventually be built in London, a prospect nobody takes seriously today.

Euston clearly has to be regenerated in some form if HS2 is to end there. But there are no options here that are both good and cheap. The final irony of the HS2 debacle will come if the next blueprint for Euston ends up looking like the original that was rejected as unaffordable in 2020. That, laughably, is probably the way to bet.