Of all the causes that the new Mayor of London should adopt in his first crucial days in office, the Garden Bridge is the most politically puzzling.

The bridge, which cost £175million, including millions from the public purse, was conjured up in less than wholesome circumstances and at best provokes a “meh” in the average Londoner.

On the surface, the politics do not add up. To cancel the scheme would signal a strong intent, a workmanlike, unsentimental commitment to running London properly. The reverse is, well, a reverse.

Here are the top 7 reasons why the Garden Bridge decision is bad politics

CGI of the planned London Garden Bridge

1. Nothing’s changed

After eight years of Conservative rule, against the trend and driven solely by the charisma of Boris Johnson, London has returned to a political compact with its most comfortable political partner. Sadiq’s first set of measures should have been to set out his stall – that he is markedly different from his predecessor, that he plays by the rules, and he plays fair. He is the self-proclaimed “Mayor for all Londoners”. So why commit to something that has all the hallmarks of Boris Johnson indulgence and elitism?

2. Money is free

Mayor Sadiq Khan has his work cut out balancing the budget and meeting his priorities (housing). His promise of a fares freeze is likely to cost TfL up to (a disputed) £1.9billion. The £30million-plus that TfL was strong-armed into contributing by Boris would be better redeployed on some of rail upgrade schemes that will be starved of cash because of fare revenue losses. As we have argued before, that money is seed money for regeneration and regeneration means new homes.

3. He’s there for the taking

The Mayor had cast doubt on the Garden Bridge before the election but now he has come round and declared it a rival to New York’s High Line. And what concessions has he wrung out to fuel his U-turn?

Fewer closures for fund-raising days – down from 12; “a strong working relationship with all of London’s parks” and a guarantee that school children will be involved with the planting. Planting fig leaves, presumably, to cover the Mayor’s embarrassment.

Read more: Are we falling out of love with the Garden Bridge?

These are no concessions, they are condescensions. And they tell all future interests heading to City Hall with a hard bargain to strike that the Mayor is a push-over. A terrible, terrible signal when he’s set himself up against London’s hard-core property developers in the arm wrestle over acceptable affordable housing levels.

4. West is best

The Garden Bridge always circles back around to the East London Thames Crossings package. The “Mayor for all Londoners” has signalled his dislike of the Silvertown Crossing and has promised (yet another) a “joined-up” review of a vision that includes Gallions Reach and Belvedere. That package was one of the Boris's best day's work .

Should Sadiq open up a front against these crossings while embracing the pointless Garden Bridge, then he is politically exposed. He’s prepared to finance a lush folly in the west but nothing (again) in the east where it actually fuels growth (and builds homes).

Investing: Mayor of London Boris Johnson has pledged more than £2million to two Tower Hamlets businesses

5. Cronyism works

The procurement process of the Garden Bridge was not exactly blessed with transparency. If this was Tower Hamlets and the man who created the bridge was Lutfur Rahman the questions would be harder and the answers would be more consequential.

The friendship circle of Boris Johnson, Joanna Lumley and designer Thomas Heatherwick who huddled up to bring the bridge into being has been examined and considered to be “littered with irregularities” – at the generous end of the critical spectrum. By signing up to the ends, the Mayor has retrospectively disinfected the means. And signalled that he’s not averse to chummying up to the beautiful people.

6. Spin wins

At the end of the statement announcing his support for the bridge , the Mayor declares: “The early days of this project clearly fell short of our expectations on transparency. I am determined to run the most open and transparent administration London has ever seen. I will let the sunshine in.” Surely we can have a brief respite, a honeymoon, between the election and the spin. Surely, the Mayor can’t spend the next four years saying one thing, doing another and assuming we won't spot the join.

Views: Julian Clary will read from his new book on The Emirates Air Line

7. Albatross symbolism

These things matter. For all its merits (and we love it), the Emirates Air Line became a symbol of Boris Johnson’s white elephant indulgences – too much money, too little thought. That may be Boris’s legacy in an Instagram.

The Garden Bridge, a glaring, expensive, unloved, impractical, inaccessible drain on the public purse in the heart of London, built on Mayor Khan’s watch could become a symbol of a similar failure of priorities.

If Sadiq – a Labour mayor – cannot build the level of affordable homes he promised but he can fund a fancy bridge for corporate functions then that’s the money shot, that’s the deal, that’s the front page of the opposition's election manifesto in 2020.