UK Prime Minister Boris Johnson. Picture: BLOOMBERG/CHRIS J RATCLIFFE
UK Prime Minister Boris Johnson. Picture: BLOOMBERG/CHRIS J RATCLIFFE

Britain’s December 12 election has been described as its most consequential in the postwar era, and that’s probably no exaggeration. But the interview question no UK leadership contender can escape has nothing to do with Brexit or the future of state healthcare. It’s simply: “What is the naughtiest thing you’ve ever done?”

Speaking to Sky News’s Sophy Ridge on Sunday, Prime Minister Boris Johnson (hardly a paragon of good behaviour) did the wise thing and refused to incriminate himself. “No, no, no. I’m not telling you,” he shot, as soon as it was clear where Ridge was going. It might be “terminally politically damaging”.

He was right to spot the trap. Answer honestly and the candidate is bound to disappoint or scandalise. Lying is worse; there’s little that escapes tabloid scrutiny in Britain. Either way, the candidate has said something he or she probably didn’t want to and changed the conversation from policy to personality.

Yet it’s not an entirely trivial question either. Despite the contradictory evidence from the US, character does still usually matter in politics (which is why Tory politician Jacob Rees-Mogg’s noxious comments on the Grenfell disaster were so damaging), perhaps even more so at a historical cross-roads. What a candidate has done before the klieg lights were trained on them says something. A youthful willingness to break rules might turn out to be a useful trait during times of gridlock or high-stakes negotiations, such as the Brexit endgame. A pattern of recklessness and self-indulgence, not so much.

So what can we learn from how a politician answers the question? Quite a lot.

The obsession with this particular interrogation started with Johnson’s predecessor, Theresa May, who was interviewed in June 2017 days before a general election in which she lost her governing majority. She’d been talking about growing up as a bookish vicar’s daughter and the question caught her off-guard. “Nobody is ever perfectly behaved, are they?” she stalled. “I have to confess, when me and my friend, sort of, used to run through the fields of wheat, the farmers weren’t too pleased about that.”

‘Thatcher in the Rye’

The answer became an internet meme. There were briefly concerns that crops could be damaged after thousands signed up to an event in Norfolk to run through fields of wheat. The trolling was endless, from “Thatcher in the Rye” jokes to a mock video game called Come Wheat May.

Her answer doubled down on the errors of a campaign that was built around her persona as a “strong and stable” leader. In fact she was a wooden campaigner, clearly uncomfortable bringing her leadership pitch to voters. Her field-of-wheat answer underscored a suspicion many had: that she was unrelatable. May later admitted that answering the question was “one of the silliest things I ever did”.

Every Conservative candidate was put through the same wringer during this summer’s leadership campaign. Andrea Leadsom, seeking to be the anti-May female candidate, told of a cross-country trip on the back of a motorbike when her parents thought she was on the bus. Sajid Javid, underscoring his ethnic roots and his ability to fight back, recounted punching a kid who’d picked on him with racial slurs. Rory Stewart said he’d smoked opium in Iran. Michael Gove was bogged down by his apologies for cocaine use.

The idea of “naughtiness” evokes a very British idea of childhood disobedience; largely behaviour without serious consequence. That’s how Johnson fielded the question when he was running for Tory leader. He scanned his unblemished early years and came up with a time when he and his sister filled a row of boots with water. He was nine.

Now that he’s prime minister running in an election, it was bound to come back with greater insistence. Of course, the real question — what’s the worst thing you’ve done — is one few of us would be comfortable answering publicly. And it’s particularly fraught for Johnson, whose past includes a string of infidelities and recent accusations of sexual misconduct (which Johnson denies).

When Ridge pressed him, Johnson could have buckled and used the question to show he’d learnt from his indiscretions, or struck a defiant Trumpian pose to rally those attracted to his mould-breaker persona. He did neither. A master of deflection, he stated that he wasn’t going there “because I would improvise an answer that I had not cleared with my handlers and I would bitterly regret it”.

He also promised Ridge that if he could think of an answer that was both “interesting” and not terminally damaging he would give it to her on their next meeting. Disarmed, Ridge moved on. Johnson is better than any of his contemporaries at using self-deprecating humour to get himself out of trouble.

What did the voter learn? Johnson, as all are aware, has exhibited behaviour that extends beyond juvenile high jinks. For some, that’s already testament to a character unfit to lead. For others, it has no bearing on whether he can deliver Brexit or govern effectively. Johnson knew the first group would not be convinced by anything he said and the latter not deterred.

Not long ago, Johnson would probably have taken the bait, going for the laugh line or striking a defensive pose. But he showed he’s developing a new muscle as a leader: a sense of restraint in the service of a bigger purpose.

And what about Labour leader Jeremy Corbyn, Johnson’s chief rival? He once insisted that his worst thing is “far too naughty to say.” But he did say: “I’m totally shocked that anyone would run through a wheat field and damage wheat. It’s a terrible thing to do.” Like Johnson, this somewhat arch deflection is pretty canny. Corbyn is behind in the polls, but he’s no ingenue when campaigning.

• Raphael writes editorials on European politics and economics for Bloomberg Opinion.

Bloomberg