In this government by Grand Designs, Johnson has spaffed the budget and the roof is leaking | Marina Hyde

In many ways it was impressive to get a whole two days into Boris Johnson’s world statesman tour before it emerged he’d tried to get a Tory donor to fund a £150,000 treehouse for his then infant son. No matter what Commonwealth/G7/ Nato posturing comes after that, you’ll have found it rather difficult to suspend your disbelief. It’s like hearing that Churchill whined and whined to get some mid-century sad-sack to buy his grandson a pony. Fine: 30 ponies.

The story of the treehouse somehow still retains the power to shock, if only as a reminder that there really is no beginning to the prime minister’s financial morality. As reported by the Times, Johnson and his wife planned to build an eye-wateringly expensive treehouse in the grounds of Chequers in autumn 2020, potentially funded by the Tory donor Lord Brownlow. “He was told it would look terrible,” a government source told the paper, yet the PM pressed ahead. It was only when the Johnsons’ security staff objected definitively on the basis that the treehouse was visible from the road that the welfare king and queen of Downing Street had to reluctantly abandon their plans. At the time, their son would have been about six months old.

Who builds a baby a treehouse for £150,000, which can currently buy you a three-bedroom semi-detached house in Wakefield? Answer that question without using a four-letter word. But then, it’s all there, isn’t it, from the mind-boggling discovery that this got all the way to design modification stage, to the reappearance of the unflushable Lord Brownlow, fast becoming the Zelig of stories in which a greedy and venal prime minister apparently takes him for a soft touch. The fact that a child’s pleasure dome was being decreed at the very same time Johnson was demanding his MPs voted against a plea to extend free school meals for the poorest children over the Christmas holidays locates it even more firmly in the realms of the grotesque. One Conservative MP, Ben Bradley, claimed the latter scheme would simply lead to increased dependency on the state. (Needless to say, Bradley has never uttered a word on the worry of increased dependency on rich donors, and continues to back Johnson to the hilt.)

Still, after the £840-a-roll gold wallpaper and the rest of the Downing Street flat refurbishment saga, it’s good to see the holder of the highest public office in the land amassing almost enough mad folly projects for a whole series of Grand Designs. Do picture the Johnsons telling the cameras: “I think we’d call our aesthetic for the project, MPs’ Expenses meets Louis Quatorze. Think duck house, except with bulletproof glass and costing a full 91 times as much.” Had the prime minister been allowed to do what he wanted, it would have been good to see the usual political interviewers make way for Kevin McCloud, who would don his hard hat of hardheadedness and observe mildly to the couple: “Well actually, you’ve gone an infinite per cent over your budget, haven’t you, because NONE OF THIS IS YOUR MONEY.” The less entertaining reality is that the MPs’ expenses era now feels like the halcyon days of taking responsibility, given that Peter Viggers, the MP who tried to get his duck house funded, never even succeeded, but did at least end up quitting when his attempt came to light, for what he admitted was a “ridiculous and grave error of judgment”.

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All of this, then, is the inescapable backdrop to the prime minister’s current gadding about on the world stage. Are Downing Street’s strategists hoping that Fake Boris (the statesman) can save Real Boris (the treehouse guy)? You can see why Fake Boris is the preferred role. This year, support for Ukraine is almost the only policy Johnson has delivered on. Everything else is either U-turned on, deliberately designed not to work, or pulled out of his arse with no thought as to what it even is, let alone how you’d achieve it. So yes – Johnson is taken seriously in Ukraine, where he is rightly perceived as top of the tree in terms of wartime allies. But it’s increasingly difficult to see how people back home are supposed to forget the grubbier reality of what he truly is. Do you really want to hear about wage restraint from a guy who wanted someone to spaff 150 grand on a treehouse?

Johnson has never received a great bounce for his leadership on Ukraine, with many holding a view along the lines of “he did what any of us would have done”. None of which is to denigrate the UK’s clearly hugely valued assistance. But it must be said that in straitening times, another view can be now heard rather more loudly than before. Recent polling suggests the mushrooming cost of living crisis has focused concern away from justice for Ukraine, with a report by the European Council on Foreign Relations (covering 10 European countries, including the UK) pointing to “a growing gap between the positions of many governments and the public mood in their respective countries”.

This could leave even Fake Johnson in trouble. Acting like a world statesman might be the right thing to do (though actually being one is obviously better). But even that could well end up a liability for a man increasingly cemented in the public imagination as selfish and feckless. What are we making sacrifices for, people might wonder, if not yet another of his vanity projects?