Britain’s greatest white elephant, HS2, was always a dud railway. It has grazed for 10 years on the Treasury lawn, and has now has been told it can stay, more dud than ever. It was symbolic this week that Boris Johnson launched HS2 not in the north but in a giant patch of Birmingham mud. Next to him stood his chancellor, Sajid Javid. They already looked like executioner and victim. Both seemed to know their “spine of the north” was as doomed as their relationship.

Johnson's real decision this week was to clear off the table any idea of HS2 going north of Birmingham

Nothing about HS2 has ever made sense. The route to Euston from Birmingham’s isolated Curzon Street, a mile from the rail hub of New Street, was chosen only because Robert Stephenson chose it in 1838. As high speed, it is daft. Each end is so ill-connected as to cancel any time saved aboard. In London the new line misses St Pancras by half a mile, thus denying the point of long-distance speed, which is to link the north with HS1 and the Channel. If HS2 patrons want to reach Europe by rail, they must wheel their suitcases down the Euston Road. Stephenson should have thought longer term.

HS2 will carry no freight. Even to attract passengers it must compete with the existing, perfectly adequate service to New Street. Euston is among London’s least congested stations. On the BBC this week, interviews with Birmingham passengers showed trains three-quarters empty.

Every recent study of the railway’s future, notably the 2006 Eddington report, demands priority for commuting. Depending on definition, trains serve less than 8% of UK journeys, and two-thirds of those are by south-eastern commuters. Northern rail passengers are mostly commuters, enduring some of the worst services on the entire network. HS2 will not help them. Railways are glorious but they are not serious contributors to economic regeneration.

As a result, defenders of HS2 have had to keep changing the argument. First it was about speed, then about capacity, now about “levelling up the north”. All this is pure spin, in support of staggering construction contracts. Speed is now discounted as energy guzzling. Extra capacity will chiefly benefit commuters from London’s northern home counties. As for emissions, HS2 admits it is going to be “carbon positive” for generations.

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Most cruel is that this project has anything to do with the north. Johnson’s belief that it will have northern voters cheering him on is puzzling. Last week’s YouGov poll showed a public against HS2 by 39% to 34%. The north and Midlands were overwhelmingly against; the one place strongly in favour was London, supporting HS2 by a massive 42% to 23%.

Londoners are not fools. If this is a white elephant, it is their white elephant. Studies by John Tomaney of University College London and others have shown that high-speed trains naturally benefit the bigger and richer end of the line. Londoners use trains like no one else. They want ever more of them, and they tend to get what they want. The reality is that HS2 is another southern-oriented, London-magnetising project. It makes as much transport sense as Johnson’s east London cable car. This Johnson partly recognises. Hence his real decision this week was to clear off the table any idea of HS2 going north of Birmingham. He has told its over-fed managers to stop there. His laughable sop to the north was a lot of bombast about electric buses, cycle lanes and pre-Beeching rail lines. Tell that to a Leeds commuter. The whole idea of “levelling up” the north is a patronising London cliche.

An indication of this was the transport minister, Grant Shapps, announcing last week that any HS2 trains north of the Midlands will have to run at the current Pendolino speed of 125mph. But since HS2 trains are non-tilting, they will have to go slower round bends. They would better be termed Low Speed 2.

Johnson is treating the north as “here be dragons” territory. The good news is that he at least turned over northern transport to a consortium of local councils. Manchester and Leeds can duly decide railway priorities for themselves. I am sure that if there is any money from “chancellor” Dominic Cummings, the north will want to spend it on urban transit and commuting. But such money can only be crumbs from the table of London to Birmingham. The north has been monumentally duped.

There was a tenuous case for bringing the UK into the high-speed rail age, mostly reliant on increased capacity from on-board signalling. As for HS2, it should only have been seen as a northern extension of HS1 from St Pancras, to link Europe with the north and Scotland. This will now never happen, except on foot down the Euston Road.

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But HS2 was always about politics. This week saw it defended entirely in the language of populist chauvinism. To Johnson it showed “spine … faith in the north”. To Shapps, it was “believing in the future of your country”, to others “an ability to get up and do something”. To be a great nation these days, you must shut your mind and indulge in a Trumpian orgy of public extravagance. Probity dissolves, vanity soars.

HS2 will sink into history, like its Victorian neighbour the Great Central into Marylebone. But the message of the new populist infrastructure has gone out. If a handful of Birmingham businessmen can claim up to a hundred thousand million pounds of public money, never can Johnson deny anyone a new hospital, school, care home or indeed crazy scheme “because there is no money”. There is always money. So gather round. Make your project high-profile and London-oriented. Think of a sum, double it, and ask Johnson if he is a patriot or a mouse. You will get billions.

• Simon Jenkins is a Guardian columnist