Donald Macintyre's sketch: Even an American with Republican Party ties was swept up in the euphoria of Jeremy Corbyn's victory

The beer hardly flowed because the heaving Sanctuary pub in Westminster had stopped serving just after 2pm.

This hardly mattered since the red T-shirt wearing Corbynistas who had triumphantly taken over the bar were more intoxicated by victory – these are people who actually know the words to The Red Flag – than they would have been by thedrink.

Which could have made things awkward for the two septuagenarian American couples trapped in the corner innocently eating their lunch a few hours after starting their UK holiday. In fact it made their day when Corbyn walked over to apologise for the noise.

“He was really personable, very comfortable with himself,” 73-year-old David Patten told me. “Anyone who can get the support from so many people at his age must have something.”

As the son of a southern Illinois collier who had been a loyal member of John L Lewis’s United Mineworkers of America, he knew a bit about labour movements. But Mr Patten was a staunch Republican, not the sort to be instinctively attracted by the stances of the most left-wing British Labour leader since George Lansbury.

“Personable” says much about Corbyn’s appeal – so far. Even more than the young supporters who had ecstatically chanted “Jez we did” when the result was announced at the QE II centre, the toilers of the “hard left” back in the 1980s were taken aback by the sheer scale of his victory. That was not only clear when Ken Livingstone breathlessly announced that he was “happier than I’ve been for 30 years”. You had to have lived through that febrile period to appreciate the historic role of Pete Willsman, for years the most left-wing member of the pivotal Conference Arrangements Committtee – charged with trying to ensure that the choice of resolutions to the then all-important party conference favoured his faction – and now the secretary of the pro-Corbyn Campaign for Labour Party Democracy.

Even Willsman did not attribute the Corbyn “bandwagon” to politics alone when I bumped into him outside the Centre. Suggesting that the same could not have been achieved by – say – Bennite MP Michael Meacher, he said of Corbyn: “He sounds like an ordinary person. He’s got an allotment. He charges next to nothing in expenses. He’s a bit of a Jesus Christ figure really. It’s his personality.”

Discounting the hyperbole, and while Corbyn’s victory speech on Saturday lacked the killer soundbite to strike a chord with the wider electorate, he certainly tried to reach out to the defeated candidates. True, he was partly defiant, especially about the media, citing the attack on “the great Ralph Miliband”, thus praising the late Marxist academic even more enthusiastically than had his son, Ed, at whom the attack had been really directed, and suggesting that Corbyn will be the first Labour leader for some time to bait the Daily Mail as much as it baits him. But his praise for all three of his opponents went beyond the merely ritual. And it was in stark contrast to that of his new deputy, Tom Watson, who didn’t even mention the runner-up Stella Creasy’s impressive 19.1 per cent showing in the contest.

Yet the deputy leader vote is arguably significant, not least because it reinforces the archaic maleness of the party’s top leadership, graphically illustrated by Corbyn, Watson and the new London mayoral candidate, Sadiq Khan, being the only platform speakers at Saturday’s special conference.

Secondly it points, perhaps more than the leadership contest, to the residual strength of the “modernising” tendency in the party. Indeed, the total percentage votes for Caroline Flint, Ben Bradshaw and Ms Creasy comes to more than that secured by Tom Watson, prime anti-Blair plotter in the last decade.

That’s only one of Corbyn’s problems. No doubt his “personality” as an ungroomed, unspun conviction politician, entirely confident in his political beliefs, was an important factor in achieving his massive majority. Ken Clarke had this, which was why it was crazy of the Tories not to choose him as leader when they had the chance. So does Nigel Farage. So did the late Charles Kennedy. But while Corbyn may have proved that this is an increasingly necessary condition of the “new politics”, is it a sufficient one?

Corbyn will be glad that Andy Burnham has agreed to serve in the Shadow Cabinet. (Burnham knew defeat was looming if not by how much. On Wednesday evening, as I waited to cross Parliament Square, I was sandwiched between the shadow Health Secretary and David Davis, who lost out to David Cameron for the Tory leadership in 2005, when Burnham told him: “I’m beginning to know how you must have felt.”)

But the party is not so overburdened with talent that he can easily afford to lose the shadow Cabinet members – including three of its best women and Ed Miliband, whom Corbyn tried to persuade on Thursday to join it – who will not now serve. And it’s not much good appealing for “loyalty”. Did not Iain Macleod and Enoch Powell – arguably with less reason – refuse to serve under Alec Douglas-Home, and when the Conservative Party was in government?

But the biggest unknown is whether Corbyn can begin to translate his massive victory in a party electorate of half a million to the wider one. Back in the Sanctuary pub, Mr Patton asked for a badge as a “memento” of this tumultuous day. A young Corbyn supporter explained they had all run out but offered hopefully to put the tourists in touch with the Bernie Sanders Democrat nomination campaign. Nevertheless, Mr Patton said he would “definitely” vote for Corbyn.

It’s a good omen, but unfortunately he’s not one of the 45 million other British electors to whom the new Labour leader now needs to take his fight.