Who paid for the refurbishment of the Downing Street flat?
The accusation that the prime minister secretly planned to have Tory donors cover the cost was just one of a string of eye-popping allegations made by his former adviser Dominic Cummings last week – but it was the thing ministers and Conservative MPs knew would stick.
“It’s the wallpaper that will get him,” is what one former cabinet minister quipped.
And sure enough, days after Mr Cummings said the PM’s plans for how to pay for renovations of the flat were “unethical, foolish and possibly illegal”, the Electoral Commission opened a formal investigation saying “there are reasonable grounds to suspect that an offence, or offences may have occurred”.
Appearing at PMQs less than an hour after the Electoral Commission‘s bombshell dropped, the prime minister trotted out his ‘nothing to see here’ defence, arguing that he’d covered the cost of the flat refurbishment and the public had better things to think about.
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But his red-faced rage in the chamber offered a flash of how he was really feeling as the former prosecutor Sir Keir Starmer led an excruciating cross-examination on who paid for what, when.
Mr Johnson doesn’t like being cornered – and he let it show.
Stonewalling in the House of Commons on Wednesday… but what happened behind closed doors between the Conservative Party, the prime minister and the Cabinet Office will be uncovered.
The Electoral Commission can demand documents, information and explanations, and could potentially seek a statutory interview with the prime minister as part of the process.
It can also issue fines of between £200 and a maximum of £20,000 for breaches of electoral law. And it can refer investigations to the police for the worst offences. There will be a paper trail of money and receipts and the truth of it will come out.
Mr Johnson is a prime minister who has had his fair share of professional and political scandal – over his relationships with women, his relationship with the truth, and his loose language. But despite all of it, his charisma and easy charm has propelled him to the highest public office in the land.
There is a reason people joke he is a Teflon Tory: nothing ever sticks.
His flaws, his faults, his dishonesty, his chaotic private life, is all priced in.
Why and how is the PM being investigated over his Downing Street flat refurbishment?
But this probe means he now faces the ignominy of being a sitting prime minister whose activities are under official investigation by the authorities – in that a line has been crossed. And the prime minister could certainly feel the heat depending on what the Electoral Commission concludes.
And it does put him in political difficulty.
Some in his party are quietly fuming. They believe that a prime minister should be leading by example not mired in scandal and involved in a formal investigation. It’s all made more acute by the proximity of the May elections.
“We should be talking about half a million people daily getting a COVID jab, not the PM’s pricy flat,” said one.
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In the immediate run, the good showing next week in the elections will give him political breathing space.
If he keeps delivering for the Conservative Party when it comes to elections, it in return will put up with the controversy he brings.
But there are bigger questions about his premiership and his legacy.
Lord Kerslake, the former head of the Civil Service, told me this week that the culture of Mr Johnson’s Number 10 will, in the end, do damage. If his administration is dysfunctional and chaotic, fire fighting and infighting, it will damage the delivery of his priorities as prime minister.
What is Boris Johnson’s flat refurb like – and how much did previous prime ministers spend?
And as for the voters, will Labour’s label of “Major Sleaze” begin to stick in voters’ minds, perhaps not next week, but over time?
There are now seven official investigations around lobbying and ministers’ conduct. There are three investigations – two within government, one from the Electoral Commission – into the flat refurbishment.
That’s potentially a lot of controversy, scandal and bad headlines to wade through over a long period.
And it raises the obvious question that if and when public trust erodes, does confidence in Boris Johnson’s government to deliver the promises he made in 2019 erode, too?
It may not be the wallpaper alone that proves terminal for this PM, but rather, the emerging culture of toxicity in his government that he cannot seem to cure.