Mark the date. Yesterday was the day the momentum shifted. Around midday, Labour leadership candidate Lisa Nandy won the backing of the National Union of Miners – a hugely resonant endorsement that also takes her closer to advancing to the next stage of the contest – and a couple of hours later she seemed to win over the dubious rank-and-file members in inner-city London.

Her soundbites about building a red bridge from “Leigh to Lewisham” were greeted with rapturous applause. Her pitch about telling a “radical, patriotic story of Britain” appealed to a diverse bunch of unpatriotic Londoners. So how did a Brexit rebel – who just three months ago was accused of “polishing a turd” in a letter to the Guardian because she voted for the EU Withdrawal Agreement Bill – win over a packed-out community centre in arch-Remainer London?

Guilt is a large part of it. Metropolitan graduates – many of whom had emigrated from the very Labour seats that turned blue at the election – wanted to hear that left-behind towns were not a lost cause. Devolution, buses and councils were Nandy's weapons of choice. And, chastened by the election result, perhaps embarrassed by years of excessive Europhilia, young Labourites could suddenly now sympathise with the Wigan MP’s Brexit compromise. Urban Labour members seem to be recognising their own hegemony in the party, and hope that voting Nandy might address the imbalance.

But, and it is a big but, the crowd was worried. One asked a question about Blue Labour. Another about refugees and immigration. They wanted to be assured that any pivot towards Nandy's towns would not result in a compromise on identity issues – immigration being paramount. To which Nandy had the perfect response.

“It's not the time to play it safe and change the men at the top,” she said, stressing the obvious facts that she is herself both BAME and a woman. She went on to recount anecdotes about her Indian father’s struggle against racists in the 1960s and 70s. Nandy can win the identity politics game by being herself and making positive statements about immigration like today's.

Perhaps, most interestingly, she likened herself to New Zealand’s Jacinda Ardern and Finland’s Sanna Marin, implying that there was an international coalition of young, liberal women fighting back against an elderly, male-dominated national populism. It was an intoxicating brew for a crowd of politically engaged Londoners. Everyone soon forgot that the day before Nandy had launched in Dagenham alongside her close ally and Blue Labour stalwart Jon Cruddas.

The international theme was continued in her response to a question on Scotland. Side-stepping the hazardous binary of unionism or independence, Nandy instead said that she was in favour of an international commission of centre-left parties examining the rise of nationalism across the world. It was a masterful piece of avoidance. Rather than risk taking a pop at Nicola Sturgeon, Nandy took a risk-free pop at Donald Trump. The ultra-sensitive issue that is Scotland was left to another day.

Last night was a small cross-section of the party. But if Nandy is winning over Lewisham, then she has a good chance of being the next leader of the party because Leigh ought to be in the bag (in any case, the former is much more important than the latter in the Labour leadership contest because that's where the members are). It is strongly rumoured that the GMB will endorse her, which would effectively see her over the line to the final round. But if, by some miracle, Nandy does not get through on the affiliates route, her team are confident that the CLPs of defeated Labour candidates across the red wall will see her home.

This is a campaign with a strong narrative. Nandy’s analysis of the election defeat is aligned with the thinking of many of the unions. Meanwhile, her identity appeals to metropolitan members. She is a fresh face to many and the second choice for supporters of other candidates – this counts for a lot in a system of preferential voting. Where she could trip up is policy. “Have you got one big offer that sums it all up?” asked one audience member. Answer that, and she could well win.