The final opinion polls for the European elections suggest Ukip is likely to attract more votes than any other party. If it lives up to forecasts, what happens next?
Success on that scale would send shockwaves through the Westminster establishment, particularly as it would demonstrate that Ukip has been done little damage by the succession of embarrassing revelations and gaffes that have blighted its campaign over the last month.
It would also leave Ukip facing the challenge of keeping up the momentum. In the short term, it will pour resources into fighting next month’s parliamentary by-election in Newark triggered by the resignation of Tory Patrick Mercer following lobbying allegations.
This ought to be a safe Conservative seat, and Ukip only scraped together 3.8 per cent of the vote in Newark at the last general election.
Ukip gaffes and controversies
Ukip gaffes and controversies
1/18 European elections poster
Party's latest EU election posters branded 'racist' and compared to BNP campaigns
2/18 Farage 'car-crash' interview
Ukip spin doctor forced to intervene as Farage falters in disastrous radio interview
3/18 Neil Hamilton
Picture Exclusive: The year is 1998. The venue is a Springbok Club meeting. The flag is a symbol for white supremacists in South Africa. And the speaker is Ukip’s deputy chairman, Neil Hamilton
4/18 Kerry Smith
Kerry Smith resigned as would-be MP for South Basildon and East Thurrock after it emerged he had mocked gay party members as “disgusting poofters”, joked about shooting people from Chigwell in a “peasant hunt” and referred to someone with a Chinese name as a “Chinky bird”
5/18 Natasha Bolter
Former Ukip member Natasha Bolter was suspected of not having the teaching qualifications she professed to, only days after it was revealed that claims of her having attended Oxford University were also false
6/18 Ukip Calypso song
Mike Reid released a single in praise of UKIP trying to control the UK's borders, only to withdraw the single after being accused of racism for singing in a Jamaican accent
7/18 Janice Atkinson
Janice Atkinson, Ukip's South East chair, pictured by protesters while campaigning in Ashford, Kent with local party chair Norman Taylor
8/18 Ukip cancels Freephone
Ukip cancels Freephone number after protesters repeatedly called to push up costs
9/18 Farage 'car-crash' interview
Mr Farage appeared to be caught out on a number of issues, from Romanian neighbours to people speaking foreign languages on the train
10/18 Ukip employs illegal immigrants
Ukip criticised after European election candidate found employing illegal immigrants
11/18 Magnus Nielsen
Ukip candidate: 'Take away the right to vote to improve election turnout'
12/18 Poster model
A “British builder” portrayed in a Ukip poster accusing EU workers of taking UK jobs turns out to be an Irish actor - aka a migrant worker
13/18 'Arrest protesters'
Ukip called for police to arrest protesters ‘who call us fascists’ ahead of showdown with anti-fascist groups in Brighton
14/18 London Live make-up
Ukip's Nigel Farage reportedly refused to go on London Live 'without professional make up-artist'
15/18 Andre Lampitt
Ukip forced to suspend the "poster boy" of its European election broadcast, after it was revealed he had posted a series of vile racist comments on Twitter
Nigel Farage says he is taking taking legal advice over “outrageous” allegations that he is responsible for more than £50,000 of “missing” EU funding that was paid directly into his personal bank account
17/18 Have I Got News For You
Nigel Farage appears in Have I Got News For You, spends the entire episode being ridiculed over expenses and party 'fruitcakes'
18/18 Anti-gay comments
Local branch chairman for Ukip defends a party's councillor candidate Douglas Denny who called gay people “abnormal” and said he wished “they stop trying to ram it down my throat”, all while discussing whether the word “sodomite” should be used
But expectations will be high that the party can pull off another stunning result in the Nottinghamshire seat. Anything short of victory, or a close-fought second place, would provoke accusations that the Ukip bubble is deflating.
The ubiquitous Nigel Farage has acknowledged that Ukip was in danger of being perceived as a “one-man band”.
In a fresh attempt to head off the charge, he will appoint a series of new spokesmen and women, many from the 20-plus Euro MPs it can expect to send to Brussels and Strasbourg.
A crucial question they will face is over which allies it chooses in the European Parliament. Will it run the risk of accusations of extremism by linking up with the likes of the Dutch PVV, whose leader Geert Wilders has equated Islam with fascism?
Strong results for Ukip will also prompt fresh bouts of introspection in Labour and Tory ranks.
Labour will try to brush off its success, and point to its expected gains in the local elections, but it would be a damaging blow to its morale.
Being beaten into second place by a party with no MPs would hardly be a sign that Labour is on the march with less than a year to go to the general election.
Ed Miliband would face fresh charges of being out-of-touch with many of the working-class voters whose support he needs to make it to Downing Street.
He would also come under pressure to match David Cameron’s promise to hold an in-out referendum on European Union membership, although Mr Miliband remains strongly opposed to the idea.
The Conservatives would be plunged into even deeper turmoil if they limp in third behind Ukip and Labour.
Mr Cameron would face renewed calls from the party’s Right to toughen its message on immigration and Europe in an attempt to win back the disillusioned former Tories who have disproportionately defected to Ukip.
The number of MPs who have advocated an electoral pact with Mr Farage’s party would be certain to grow. The Ukip leader indicated this week he was open to the idea of local deals with anti-EU MPs (Labour as well as Tory) if they “genuinely want this country to be free, independent and self-governing”. He said: “I would do a deal with the devil if it got us a referendum.”
If the polls have got it wrong and Ukip comes second, that would still be a remarkable performance for an “outsider” party.
But it would still be seen as disappointing given the way Mr Farage and his cohorts have talked up their prospects. His enemies would then revive images of bubbles bursting and the Ukip boss would face challenging questions of “what next?”