Nigel Farage’s expected victory will have the biggest impact on the crisis-ridden Tories

Nigel Farage’s Brexit party stood at 32% in an average of four polls on Tuesday, with one putting the party on a remarkable 37%. Its victory is expected, and a winning proportion into the 30s is probably the minimum.

Remember that Ukip, led by Farage, topped the 2014 European election with 27.5%. Yet a year later, the party won only one seat at Westminster in the general election. Nonetheless, any total of 35% or more sends a clear message: a large proportion of the public want Britain out of the EU and Theresa May out of Downing Street.

In the likely event of a Conservative wipeout and Brexit party triumph, expect to hear Tory calls for a leader to replace May who can tack to the right and mop up the millions of Brexit party votes. Arguably, something similar happened in 2015, when David Cameron made his fateful referendum promise.

Labour will want to finish a healthy second, but could well end up third

Labour was polling in the mid-30s in mid-April, but has been tumbling ever since, from 24% at the time of the local elections on 6 May to 21% on the current rolling average. Those figures are a disappointment for a party leadership that prides itself on campaigning well and exceeding expectations at the ballot box. Some recent YouGov polls put Labour in third place, behind the Liberal Democrats, on as low as 15% or even 13%.

Labour achieved 25.4% in 2014, a result the party is likely to struggle to match now. A score in the low 20s – or worse – will demonstrate Labour has lost significant support to unambiguously anti-Brexit parties, as well as to the Brexit party. Third place would be a psychologically significant blow.

Second referendum campaigners are already arguing the party has been punished for its long and deliberate ambiguity on Brexit. The leadership’s counter-argument will be that European elections have always been a place for protest voting.

It will be a bad night for the Conservatives, but it could be a traumatic one

The party’s predicted share of the vote has fallen from 20% in mid-April to less than 15% at the time of the local elections to 11%, reflecting deep internal splits and a non-existent campaign. On Wednesday, YouGov put the Tories on a stunningly low 7%.

That would be unprecedented for a governing party. The closest equivalent is the 2009 European elections, in which Labour scored 16% and came third. A year later, Gordon Brown was kicked out of No 10.

The result this time will inevitably be interpreted as a referendum on May’s leadership and her failure to deliver Brexit. But do not underestimate the emotional impact if the Conservatives finish behind the Lib Dems, or even fifth behind the Green party.

Less a judgment from the electorate, more a catastrophe.

Small parties do better – with one exception

The already buoyant Lib Dems will hope to come second and expect to outdo the Tories, given their “Bollocks to Brexit” campaign has taken the party to about 15% in the polls, and 19% on some projections. Remember, this is a party recovering from the coalition years – the Lib Dems scored 6.9% in 2014.

Change UK, which has fallen as low as 1% in some polls, will probably claim it is pleased if it achieves its 4% average polling figure. Whatever the result, Change UK must surely be heading towards a deal with the Lib Dems, or risking obsolescence.

The Greens polled about 8% in 2014 and 2009 and will hope for a couple of points more after a period of mounting environmental concern. Beating the Tories would be a real fillip.

Keep an eye on Scotland too, where polling has the SNP as high as 38%. That would be sharply up on the 29% it achieved in 2014, as Conservative and in particular Labour votes tumble.

Translating the results into second referendum figures will be frustratingly difficult

The simplest route here is to add up the share of the hard leave parties – Nigel Farage’s Brexit party and what is left of Ukip – and compare that with their remain counterparts: the Lib Dems, Greens, SNP, Plaid Cymru and Change UK.

On this crude measure, the results will be close, but at this stage leave is expected to be ahead. A YouGov survey for the European Council on Foreign Relations, published in the Guardian, put the figures at 36.1% for leave and 37.5% for remain.

The challenge is how to account for Labour and Conservative voters. The BBC’s election analysis suggests 75% of Labour voters and 50% of Conservatives are remainers. But such calculations are inherently unsatisfying as it proposes a subdivision not immediately obvious from the ballot paper. All this means any attempt to read the election as a proxy second referendum would be open to challenge.

• This article was amended on 23 and 27 May 2019. An earlier version said YouGov data “had only 37% of Labour voters wanting to remain and only 6% of Tories”. These figures were misinterpreted from the source data and have been removed. We also mixed up the remain and leave figures in the the European Council on Foreign Relations survey, which have been corrected.