At a lavish party for Nigel Farage at London’s Ritz Hotel five months after the 2016 referendum, the man himself predicted a “big, seismic shock in British politics” like Donald Trump’s “total revolution” in the US.

Farage told the 100 guests – friends, politicians and journalists (including me) – the UK’s problem was “still being run by the career professional political class”. He feared it would block Brexit. With Ukip seen as a basket case, in the margins of the event, his allies discussed launching a new, online-based movement based on Italy’s Five Star.

The Brexit Party is now up and running, the cleverest piece of political branding since New Labour. European parliament elections on 23 May offer the perfect opening; coming almost three years after the referendum, they validate Farage’s repeated claims that politicians would betray the public. Ukip, a home for Islamophobes and misogynists who dismiss jokes about rape as “satire”, makes Farage look respectable. Not surprisingly, the opinion polls suggest his new party is on course for a famous victory. His “big seismic shock” is on the cards.

The only politician who can prevent it is not Theresa May – ministers are increasingly gloomy about her prospects of securing commons approval for her Brexit deal in time to call off the elections. It is Jeremy Corbyn. But to mobilise and hoover up the Remain vote, he will have to do something he is reluctant to do: make a stronger commitment to a Final Say referendum. A YouGov survey for the People’s Vote campaign suggests an explicit referendum pledge would raise Labour’s ratings to only three points behind Farage’s party, while fighting on Corbyn’s policy of a customs union would leave Labour trailing 10 points behind it.

Corbyn’s close allies insist that while he is keeping a public vote on the table, an unequivocal pledge could alienate Leave voters in the north and Midlands. They argue that Labour support has not collapsed like the Tories’ in recent polls, so Corbyn’s “constructive ambiguity” still allows him to appeal to both Remainers and Leavers. The allies keep their eyes on the main prize: the general election they believe is likely later this year (probably called by May’s successor rather than her being defeated in a commons vote of no confidence). They point out that 35 of Labour’s 45 target seats and 16 of the 20 most vulnerable Labour-held seats in England and Wales, voted Leave in 2016.

Farage launches his new Brexit Party: in pictures Show all 10 1 /10 Farage launches his new Brexit Party: in pictures Farage launches his new Brexit Party: in pictures Nigel Farage speaks at the launch of his new Brexit Party's campaign for the European elections Reuters Farage launches his new Brexit Party: in pictures Brexit Party candidate Annunziata Rees-Mogg, sister of Conservative MP Jacob Rees-Mogg, speaks at the launch AFP/Getty Farage launches his new Brexit Party: in pictures A supporter waits for Farage to speak AFP/Getty Farage launches his new Brexit Party: in pictures Supporters wait for Farage to speak AFP/Getty Farage launches his new Brexit Party: in pictures Farage's socks Reuters Farage launches his new Brexit Party: in pictures Farage and prospective candidate Annunziata Rees-Mogg wait at the launch AFP/Getty Farage launches his new Brexit Party: in pictures Supporters listen as Farage speaks AFP/Getty Farage launches his new Brexit Party: in pictures Free T-shirts for all attendees AFP/Getty Farage launches his new Brexit Party: in pictures Posters on the seats for supporters of the Brexit Party AFP/Getty Farage launches his new Brexit Party: in pictures A safety sign is pictured AFP/Getty

However, these statistics are misleading. Research by University College London found that “it is clear that even in heavily Leave-voting areas, the majority of Labour voters were Remainers”.

There is a risk Corbyn alienates some of the two in three Labour voters who want to Remain if he fails to promise a referendum. He would also be missing an opportunity to halt Change UK (The Independent Group) in its tracks; instead, more Labour MPs might join it. Despite that, as one Labour frontbencher told me: “Jeremy will probably continue to sit on the fence, even though he could spoil Farage’s party by getting off it.”

Farage’s other enemies are also playing into his hands. The anti-Brexit parties – the Liberal Democrats, Change UK, Greens, the SNP and Plaid Cymru – have not agreed a joint ticket, so their impact will be diluted. Although the European elections are fought under proportional representation, the system used favours big rather than small parties.

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The arrival on the scene of Change UK is a breath of fresh air for our stale politics. On the face of it, the European elections provide a perfect launchpad for the party. But the 11 former Labour and Tory MPs who formed it want to preserve their identity as the new brand in the centre rather than help elect Lib Dem or Green MEPs. It is a pity that these parties have not joined forces, as Vince Cable suggested; that would pose more of a threat to Labour, and strengthen the hand of shadow cabinet members urging Corbyn to go further on a referendum. The smaller parties should try to agree a non-aggression pact to maximise the chances of pro-Europeans winning seats.

They should not fight the European elections on an anti-Brexit ticket but on a pro-referendum one, which would widen their potential support. Calling for Remain can be portrayed by opponents as anti-democratic, but what can be more democratic than asking the people? The European elections cannot be a substitute for a new referendum, but can become a stepping stone to one.