Jeremy Corbyn’s middle name is Bernie. A friend posted a picture of his Islington North postal ballot paper on Facebook the other day, and there, between ‘CLARK, James Tovey’ and ‘FOSTER, Michael Adam’, was ‘CORBYN, Jeremy Bernard’. It's odd that nobody seems to have pointed this out when Bernie Sanders was over here last week, promoting his new book.

Introducing him at Brixton Academy on Friday, David Lammy instead echoed Dan Roberts’s Guardian profile of ‘a leader who was at first ignored, then ridiculed, and now reviled by the establishment’, and ‘has seen a last-minute surge in the opinion polls that threatens to upset a complacent opponent’.

‘Could the same thing be about to happen here?’ asked Lammy, whose hostility towards Corbyn over Brexit seems to have mostly melted away, in the bright heat of Labour’s general election campaign. ‘Let’s hope so.’

The sell-out crowd roared, and we rose to our feet as one, in a self-conscious imitation of the Sanders stadium rallies we watched on the news this time last year. The people wanted an emphatic endorsement of Corbyn, but Bernie wanted to talk about America. It was only after he’d made the case for the radical transformation of the Democratic Party into a popular movement – directing its energies away from the Clintons’ strategy of securing ‘big money contributions’ and towards a ‘progressive majority’ of young, working class, left-behind and first-time voters – that he smiled, paused, and said, ‘I understand that there may be a similar process taking place here today.’

Much of what he said chimed with Corbyn’s answers on Question Time, though, which began as the Brixton event came to an end: his emphasis on an increased minimum wage, free university tuition and the possibility of paying for such things with a modest increase in corporate taxation; his criticism of politicians unwilling to participate in the cut and thrust of election campaigns. The most striking difference between their approaches was in the detail: Corbyn’s responses were flecked with reassuringly small-scale specifics; Sanders’s speech soared with the unimaginable sums Trump intends to squeeze out of ‘life and death programmes’ for the poorest people in America, into the pockets of the 1 per cent.

‘Two point five trillion dollars!’ he cried, arms windmilling in the way we’d hoped they would. He’s a hugely appealing presence, for a politician, springing up from his chair to answer audience questions (‘I prefer to stand – I realise that for some other folks like David here, it’s difficult’) and wrapping familiar sentiments in a rhetoric so genuinely unusual that it occasionally felt like it really could be the basis of a different kind of politics. ‘You probably know people suffering from addiction to drugs or alcohol,’ he began. Then: ‘Well, we need to tell millionaires that their addiction to greed is a sickness, and sick people should not be allowed to rule the world!’

Both politicians’ projects depend on our willingness to believe in Bernie’s ‘progressive majority’, the dormant ‘non-voters’ who, Corbyn’s supporters hope, ‘will awake from their slumber and vote for him’. More than two million people registered to vote after Theresa May called the election; 250,000 under-25s signed up on the day registration closed.

‘I have a text from a man who’s just about to appear on Question Time,’ Lammy said, before reading Corbyn’s message: ‘David, can you wish Bernie solidarity and thanks, and a huge welcome to Britain. And after Thursday, can he come back when I form a new government, and this country gets serious about social justice.’ Over shrieks of approval from the crowd, Sanders responded: ‘Please text back Mr Corbyn: I will be more than delighted.’