SARAH VINE: While Rayner and Mordaunt were at each other like a pair of fishwives, Farage just giggled in the BBC's election debate

A week is a long time in politics, but it took less than 48 hours for Rishi Sunak’s fortunes to change – perhaps irreversibly. Having secured an unexpected advantage over Keir Starmer in Tuesday night’s debate on ITV, by teatime on Thursday his victory had evaporated.

Not since Prince Andrew decided it was a good idea to sit down with Emily Maitlis and tell her all about his sweat problem has a public figure made such a catastrophic error of judgement.

Why? Why would any politician in their right mind leave the 80th anniversary D-Day celebrations early, let alone to conduct a pre-recorded interview with ITV?

‘I stuck to the itinerary that had been set for me as Prime Minister weeks ago - before the election,’ he insisted, which in many ways made it worse, only emphasising his tin ear.

It was excruciating. No politician should put their career before their public service. Thoughtless, disrespectful and above all, incredibly rude.

And so it was against this distinctly unfavourable background that Penny Mordaunt took to the podium for Team Tory last night in the first BBC debate, hosted by Mishal Husain.

Nigel Farage had already dubbed it Sunak’s ‘Gillian Duffy moment’ (a reference to Gordon Brown’s infamous hot-mic gaffe where he called Rochdale voter Ms Duffy a ‘bigoted woman’), while Labour was quick to issue posters that simply read, ‘He left them on the beaches’ above a silhouette of the PM scuttling out of view.

Mordaunt is of course MP for Portsmouth, a town with many military connections, and distinguished herself with her sword-carrying duties in her role at the Coronation. She is also one of the top contenders to replace Sunak as leader of the party if the polls prove correct on July 4.

It’s not easy going in to bat for someone you’re plotting to replace, especially when he’s just handed every opponent a loaded gun. Labour’s Angela Rayner, the SNP’s Stephen Flynn, Daisy Cooper from the Lib Dems and the Greens’ Carla Denyer, plus Rhun ap Iorwerth from Plaid Cymru and – last but by no means least, not long to this election party - Reform’s Nigel Farage were licking their lips in anticipation.

The first question did not disappoint. D-Day, armed forces, how would the parties ensure national security? Rayner, standing next to Mordaunt (strong hair energy in that corner) was surprisingly measured; no mention of Sunak’s catastrophic unforced error. It was left to Farage to bring this up, which he did in his typically bumptious way, accusing the PM of being ‘very unpatriotic’.

Mordaunt looked almost grief-stricken, her face pale beneath her giant Thatcher-style blow-dry. What Sunak did was ‘completely wrong’, she conceded. But any sense of contrition was short-lived.

She turned her ire on Rayner, accusing her of abandoning the nuclear deterrent, jabbing at the air in a manner than can only be described as mildly unhinged.

Rayner, dressed inexplicably in a bright-red puff-sleeved prom frock, regarded her political foe with amused bafflement. She was surprisingly restrained in her response, as though dealing with an over-emotional teenager.

Husain steered the question back to the other four, who for the most part gave suitably dreary answers - apart from Rhun ap Iorwerth, who made a salient point about the irony of the PM proposing a new National Service while showing such disrespect for the forces himself. Unsurprisingly, that went down well.

This seemed to be a classic BBC Leftie audience. They appeared especially delighted with the Lib Dems’ Daisy Cooper, whose concerned geography-teacher vibe played well to the gallery. Rhun ap Iorwert’s square-jawed Welsh socialism was popular too. But ultimately the whole thing was, well… a bit dull and extremely predictable.

It wasn’t helped by the fact that Husain just wasn’t very good at controlling the conversation. Time and again, Rayner and Mordaunt dominated the discussion, going at each other like a pair of fishwives - while Farage, at the other end of the line, giggled and made rude faces. Husain seemed unable – or maybe unwilling – to shut them up.

When the others did get a chance at the microphone, it was short-lived, and often interrupted by Farage, who seemed to struggle to understand the difference between debating and heckling.

That said, he was the one person who brought a bit of spark to this otherwise lacklustre debate. He’s as much a showman as he is a politician, and his closing statement was a masterclass in pub politics. As the credits rolled, Mordaunt looked mightily relieved. She survived. For now.