Heading into the EU elections on this day next week, the British political establishment is faced with a surreal fact – that for the first time in a national election, neither the Conservatives nor Labour are expected to be the “winning” party.

UKIP holds the lead in EU elections voting intention in the majority of polls published since late April, with some tentative indicators too that the Liberal Democrats could be pushed down into fifth place by the Greens. Whilst this paints a picture of mainstream political collapse, we must remember that this is nothing new; the combined “protest vote” of parties other than the main three was 42% the last time we voted for our European representatives in 2009.

 It’s going to be an odd state of affairs if UKIP returns the largest number of MEPs to Brussels but is still unable to secure control of a single local authority.

This is an exciting time for people who want to see UKIP succeed, as well as being an exciting time for those wanting to see it fail.

A central feature of the elections to watch, aside from the inevitable excitement likely to be generated in the chattering classes should UKIP come first, will be whether the collective share of the protest vote expands further into mainstream territory this time around. Whether it will – and what proportion of it will owe to UKIP hoovering up votes from the other fringe parties – will be a measurement looked at by electoral strategists on all sides.

The stronger the anti-establishment narrative at the elections, the more scope UKIP will hope they have to retain voters as we enter the final year of the Coalition. Nigel Farage will remember that scoring 17% and coming second at the EU elections in 2009 provided little comfort for the measly 3% his party achieved a year later at the General Election.

The issue of immigration has proved to be ripe for the picking for Farage, no matter how divorced from reality his claims may sometimes be (the ONS yesterday showed that the number of Romanians and Bulgarians getting British jobs has in fact gone down since border controls were relaxed in January). The party’s 2014 Manifesto, titled “Create an Earthquake”, focuses on protection from exterior national threats to jobs and housing, further embellishing a portfolio of solutions to policy areas which matter to people far more than Europe – areas which were lacking any coherency in its 2010 campaign.

Nevertheless, UKIP must overachieve in a week’s time if it wishes to create the earthquake it’s hoping for.

The EU elections are a poor test of party loyalty; a recent Survation poll of London voting intention for both the EU and local elections showed UKIP’s share of the vote to drop from 20% for the former to 11% for the latter. UKIP’s general popularity is lower in London than many other areas of England, but it’s an early indication of how the EU vote is likely to translate as people size up whether or not they’d welcome local control from the party.

This, arguably, is the Achilles Heel of UKIP. If the party has any hope of returning an MP to Westminster at the General Election in 2015, a broad spread of the vote and the winning of a scattering of councillors is simply not sufficient – it needs to demonstrate that it can win overall control of an authority locally.

In an electoral system different to the European Parliament, which luckily for UKIP is proportional to overall shares of the vote, the British Parliament requires prospective MPs to get the largest number of votes in each of the 650 constituencies represented. This means that the Lib Dems, who may poll nationally at around 10%, will still return MPs next year because they have such strong support in specific localities where they might get 40-60% of the vote.

UKIP on the other hand have a broad, but unfocused base of support, meaning that whilst they may well poll higher than the Lib Dems nationally in 2015, the evidence is still dubious as to whether they come out top in any individual constituency battle. It’s a system determined by consolidated and localised support, and it’s for this reason that some might argue UKIP’s electoral performance locally next week on 22 May to be far more important than if it manages to pip Labour in the EU polls.

It can conversely be argued, of course, that should UKIP manage such a feat, this risks being a poisoned chalice for a brand so well rehearsed in anti-establishment. Nothing erodes populism faster than the inevitable drag effects of incumbency, and some UKIP members may well prefer being a part of an outspoken “thorn-in-the-side” political organisation that isn’t actually burdened by the accountability of running local council services. Indeed, for a party that has survived numerous scandals which would offend public sensibilities had they happened to any of the main three parties, perhaps remaining sufficiently outside of the British political infrastructure is exactly what is intended.

Regardless, it’s going to be an odd state of affairs if UKIP returns the largest number of MEPs to Brussels but is still unable to secure control of a single local authority. This is an exciting time for people who want to see UKIP succeed, as well as being an exciting time for those wanting to see it fail.