No, no, this is an uncharacteristic mistake. Keir Starmer’s welcoming hand on Natalie Elphicke’s shoulder is a picture his enemies will relish as proof he was never really a Labour man. Where was the steadying hand of a Pat McFadden or Sue Gray to make him stop and think: just say no? It is easy to see how, in the hectic frenzy of 24-hour Westminster, the astonishing gift of the most comically unlikely MP crossing the floor at PMQs looked irresistible. The wow factor was a great theatrical coup, a sugar-rush of triumph. God knows what’s in it for her; some revenge for an unknown slight? Or a last-minute bid to dissociate herself from her nasty party? Maybe she’s just part of the great chicken run of “gissa job” Tory MPs clambering off before the Tory ship goes under. The notion that she’s defecting because Rishi Sunak has abandoned the centre ground, as she claimed, is laughable. She belonged to the Common Sense faction of Conservative MPs, one of the most rightwing cabals of culture warriors, chaired by Suella Braverman’s svengali, John Hayes, who would topple over if he moved any further right: fellow members include Jonathan Gullis, Edward Leigh, Andrew Rosindell, Danny Kruger and, formerly, Lee Anderson, until he scarpered to Reform. If she’d brought that whole crew over to crash his party, would Starmer have embraced them too? Policy discipline has been the hallmark of Starmer’s phenomenal revival of the party: ejecting anyone off-message, imprinting his brand on all candidates duly paraded, word-perfect, in recent byelection victories. Neil Kinnock, who expunged Militant, knows a thing or two about defining a party: “We’ve got to be choosy,” he told The Week in Westminster on BBC Radio 4. “It’s a very broad church but churches have walls and there are limits.” Glee over Elphicke plainly abandoned any intellectual definition of what it is to be “Labour”. Where was Elphicke’s line-by-line recantation of all her past atrocious sayings? Kate Osamor was given back the whip super-fast on the same day: she had long apologised for linking Gaza with the Holocaust. Diane Abbott must be taken back at once; she too has profusely apologised for making crass comments in April last year that Jewish, Traveller and Irish people don’t suffer discrimination as black people do. As long as Jeremy Corbyn stubbornly refuses to accept the Equality and Human Rights Commission’s findings on Labour antisemitism during his time as leader, he exiles himself. This is a one-day-wonder: Elphicke is not standing again and will be as forgotten as Christian Wakeford (if the name escapes you, he defected to Labour in 2022). Dr Dan Poulter’s hop across the floor last month drew a loud raspberry from inside the NHS. He said he could no longer look his NHS colleagues in the eye, after years, even as a health minister, of voting through the most brutal NHS funding cuts ever. But he’s the kind of Tory penitent Labour can accept, while Elphicke is off the scale. Defectors to the enemy are rare. The Tories, in post-Brexit turmoil, ejected a host of remainers, from Ken Clarke to David Gauke, Philip Hammond, Nicholas Soames and others, but they didn’t cross the floor, and some later had the whip restored. Politics is nothing if not viscerally tribal: look at the contempt in the Tory press today. But rats get barely more welcome from the bench they join, after the photo-op is over. Whips will be arm-twisting MPs to sit next to new-girl Natalie. Winston Churchill, who ratted and re-ratted, was a lonely, untrusted figure on the Tory benches he rejoined, until proved right about Hitler. Shaun Woodward, who abandoned his failed Tory party in 1999, had a chilly welcome from Labour, except from Tony Blair, who gave him the safe seat of St Helens South, high on the deprivation index and hardly suited to the only Labour MP with a butler. He never belonged. The public are ambivalent about party loyalty: they don’t like turncoats, but they don’t like servile obedience to whips either. They hate parties – a Europe-wide phenomenon, says Prof Tim Bale, chronicler of the decline in party loyalty. Perversely, they want independent-minded MPs yet they don’t elect parties riven by chaotic infighting. They complain about the quality of politicians, says Prof Rob Ford, yet refuse to take part, only a pathetic 1.5% of the British electorate deigning to join one of the three major parties. Most people do define themselves as right or left of centre as an identity, he says, but agree with a ragbag of policies that cross this line. Look at the very long list of MPs, mainly men, behaving badly, in a litany of sexual harassment, bullying or selling influence, but are MPs more aberrant than average? Ford says he often wonders – but no one knows: “If any organisation came under the same brutal scrutiny as MPs, how many would be exposed?” This is a one-day stumble for Keir Starmer. Elphicke will vanish into pub-quiz land. But, as rumours abound, other jumpers may follow: her admission to the party has set the lowest bar: if not her, can anyone be turned away? In the flutter of excitement, Labour high command momentarily forgot they are the masters now (almost). They need no defectors: all that matters is defecting voters, and I doubt Elphicke brings many. Dignity matters, and it devalues Labour membership to accept the dregs of the defeated party opposite. Starmer may regret this precedent in tough times ahead when trying to impose policy discipline on any future Labour mavericks. Polly Toynbee is a Guardian columnist