Perhaps the most scathing line of the night was the title. It was called Our Next Prime Minister and as the hour wore on, those four words sounded increasingly like a rebuke to the nation. Look at us, they seemed to say: a fabled country with a long, proud history and one of these five jokers is actually going to be our next prime minister.

It was a painful hour, delivered via a format that featured too much cross-talk and too little cross-examination, that saw the candidates perched awkwardly on gameshow stools, repeatedly talking over each other and failing to answer the often sharp and pointed questions from members of the public.

It seems invidious to pick out the most cringeworthy moment, since there were so many contenders for that prize, but surely one of the most toe-curling segments came in response to a question about Islamophobia from Abdullah in Bristol. Each of the five men who would be PM began boasting of their Muslim-friendly credentials, from Boris Johnson’s invocation of his Muslim great-grandpa to an earnest salaam alaikum from Rory Stewart. Even Sajid Javid managed to sound oddly detached when he spoke of having “many Muslim friends and family.”

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And yet, for all that, the hour was not entirely uninformative or unproductive. That Islamophobia section, for example, bore valuable fruit when Javid extracted an impromptu pledge from his colleagues to back an external inquiry into anti-Muslim prejudice in the Conservative party. Whoever wins will not be able to shake that off, and it could have far-reaching consequences.

But there were other moments that were revealing. Johnson may be unstoppable as the bookies’ favourite, but he hardly resembled the charismatic vote-magnet his supporters like to imagine. His defenders will doubtless say he was reining it in, opting for a safety-first strategy of restraint, making no jokes, starting no rows, doing no harm. But he came over as lacklustre and badly flawed.

Twice he failed to remember Abdullah’s name: not ideal when trying to demonstrate that he’s no anti-Muslim bigot. He ignored the moderator, Emily Maitlis, so often, she was eventually forced to ask: “Can you hear me, Mr Johnson?” Again, not a good look for a party with an all-male top table.

More substantively, he flailed on Brexit, unable to offer any coherent idea, let alone plan, for how he would deliver British withdrawal from the European Union by 31 October, still less cope with the multiple consequences of crashing out without a deal. Pressed on how he would maintain an open border between Northern Ireland and the Irish Republic, he suggested a “standstill” in the current arrangements, and then tossed out a reference to “Gatt 24 or whatever it happens to be.” He sounded like he was winging it, hoping that the so-called Gatt 24 provisions would ensure tariff free trade with the EU, when they ensure no such thing: both sides would have to agree a trade deal first.

He came unstuck again and again. His signature tax promise, raising the threshold for the higher rate – a move that would benefit high earners – was reduced to a mere “ambition”, downgraded from a policy just eight days after launch.

More telling still was when Maitlis forced the former foreign secretary to listen back to his own words, quoting his off-the-cuff suggestion that the British-Iranian citizen Nazanin Zaghari Ratcliffe had been training journalists in Iran. “It didn’t make any difference,” said Johnson. And yet those words of his were cited by the Iranian judge who extended her jail sentence. “Words have consequences,” said Maitlis acidly.

It’s moments like those that Johnson has been so desperate to avoid in this campaign. The debate may not be enough to deny him the job he craves, but it will have punctured the belief of those Tories who insist “Boris” is a political magician, able to hypnotise the electorate with his sheer charisma. He didn’t look like that on Tuesday night.

Not that anyone else was able fully to exploit the opening Johnson presented. By his actions, Rory Stewart confirmed that he is a spy: he’s clearly acting as a sleeper agent within the Tory leadership contest both for the cause of remain and for the opposition parties. Repeatedly, he separated himself from the other four, casting them as peddlers of fantasies and lies. “The difference between me and the other candidates,” he said, “is I’m not setting red lines and making impossible promises on TV.”

Remain-minded viewers would have cheered as Stewart mocked the pledge to deliver either a new withdrawal deal or a no-deal Brexit by Halloween. Brussels won’t provide the former and parliament will block the latter, he said, settling into his favourite niche as the fearless teller of truths.

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But he performed the same service on domestic policy too, sounding like a proper social democrat when he insisted the priority should be public services, not tax cuts. “I’m not thinking about promises for the next 15 days, but for the next 15 years,” he said in the closest thing this debate had to a zinger. At moments like that you had to remind yourself that not only is Stewart seeking to lead the Tory party, rather than a new centrist grouping, but that he too is advocating a pretty hard Brexit, in the form of serving up again the “cold porridge”, as Michael Gove called it, of Theresa May’s withdrawal agreement. Any liberals still cooing over Stewart will have felt their infatuation deflate when Stewart unaccountably declined to criticise Donald Trump’s bigoted Twitter baiting of Sadiq Khan. (As for his body language, Stewart was caught striking a series of what seemed to be tantric yoga poses, perhaps picked up on a drowsy afternoon in Kandahar.)

Gove meanwhile leaned into his role as the contest’s swot, insisting he had a plan for every eventuality – surely an audition for a detail-heavy top job under Johnson, to compensate for his future boss’s obvious deficiency in that area. Jeremy Hunt still seems unclear whether he is running from the right or left, and so left little mark.

It was left for someone else entirely to speak for the nation. When Carmella from Southampton – anxious that a no-deal Brexit would put her husband out of a job – rolled her eyes as the candidates failed to reassure her, or even answer her question, she found the eloquence lacking on stage. One of these as our next prime minister, her look seemed to say: what have we done to deserve that?