Diane James will not formalise her nomination as Ukip leader just 18 days after she was declared Nigel Farage's successor.
The shock twist was confirmed after MEP Ms James released a statement saying she was quitting because she did not have "sufficient authority" to make the changes she thought necessary.
Her departure has led to immediate speculation that Nigel Farage could come back to lead the party for a third time in his political career.
In her a statement Ms James said: "It is with great regret that I announce that I will not be formalising my recent nomination to become the new leader of the party with the Electoral Commission.
"Having won the enthusiastic support of party members, I was nominated by them as the new leader at the recent Ukip Bournemouth conference.
"Since that time, I have been in discussion with party officers about the role. It has become clear that I do not have sufficient authority, nor the full support of all my MEP colleagues and party officers to implement changes I believe necessary and upon which I based my campaign.
"For personal and professional reasons, therefore, I will not take the electoral process further."
Ukip chairman Paul Oakden said he had confirmation of the resignation, adding: "I will now look to convene an emergency meeting of our National Executive Committee to confirm the process for electing Diane's replacement."
Suzanne Evans, one potential contender to take over, told The Independent: "There's no leadership contest at the moment.
"I'm not able to rule anything in or anything out."
Ms Evans led Ukip for a few days the first time Mr Farage resigned and won praise after writing the party's election manifesto, but fell out of favour when Mr Farage returned.
Ukip's only MP Douglas Carswell, also seen as a possible candidate, simply tweeted: “In the middle of supper. Not taking calls about Ukip stuff. It's shepherds pie, by the way.”
MEP Steven Woolfe, the party's immigration spokesman who was ruled out of the previous contest due to a bureaucratic error, is said to be ready to take over if called upon.
London Assembly Member Peter Whittle has also been praised following a competent performance during the London mayoral election.
Some Ukip insiders have suggested a new snap-leadership contest could be held to appoint someone to the top job rapidly.
Early reports suggested Ms James was leaving due to family reasons. She had been the frontrunner in the leadership contest, which ended on 16 September and saw her declared winner after taking 8,451 votes, some 46.2 per cent.
Nigel Farage's most controversial moments
Nigel Farage's most controversial moments
1/12 When he unveiled that 'breaking point' poster during the referendum
Mr Farage was accused of deploying “Nazi-style propaganda” when he unveiled a poster showing Syrian refugees travelling to Europe under the next “Breaking point”. Users on social media were quick to compare the advert to a Nazi propaganda film with similar visuals and featuring Jewish refugees. The poster was particularly controversial because it was unveiled the morning of the killing of Labour MP Jo Cox
2/12 When he said he’d be concerned if his neighbours were Romanian
In May 2014 Mr Farage was accused of a “racial slur” against Romanians after he suggested he would be concerned living next to a house of them. “I was asked if a group of Romanian men moved in next to you, would you be concerned? And if you lived in London, I think you would be,” he told LBC radio during an interview. Asked whether he would also object to living next to German children, he said: “You know the difference”
3/12 When he said the EU campaign was won 'without a bullet being fired'
Nigel Farage has said the next Prime Minister has to be a Leave supporter
4/12 When he resigned as Ukip leader and came back days later
After failing to win the seat of South Thanet at the general election, Nigel Farage stepped down as Ukip leader – as he had promised to do during the campaign. Days later on 11 May he “un-resigned” and said he would stay after being convinced by supporters within the party. We’ll see how long his resignation lasts this time
5/12 When he blamed immigrants for making him late
Mr Farage turned up late to a £25-a-head ‘meet the leader’ style event in Port Talbot, Wales in December 2014. Asked why he was late, he blamed immigrants. “It took me six hours and 15 minutes to get here - it should have taken three-and-a-half to four,” he said. “That has nothing to do with professionalism, what it does have to do with is a country in which the population is going through the roof chiefly because of open-door immigration and the fact that the M4 is not as navigable as it used to be”
6/12 When he wanted to ban immigrants with HIV from Britain
Mr Farage has used his platform as Ukip leader call for people with HIV to be banned from coming to Britain. Asked in an interview with Newsweek Europe in October 2014 who he thought should be allowed to come to the UK, he said: “People who do not have HIV, to be frank. That’s a good start. And people with a skill.” He also repeated similar comments in the 2015 general election leadership debates
7/12 When he defended the use of a racial slur against Chinese people
Defending one of Ukip’s candidates, who used the word “ch**ky” to describe a Chinese person, Mr Farage said: “If you and your mates were going out for a Chinese, what do you say you're going for?" When he was told by the presented that he “honestly would not” use the slur, Mr Farage replied: “A lot would”
Lintao Zhang/Getty Images
8/12 When he said parts of Britain were ‘like a foreign land’
The Ukip leader used his 2014 conference speech to declare parts of Britain as being “like a foreign land”. He told his audience in Torquay that parts of the country were “unrecognisable” because of the number of foreigners there. Mr Farage has also previously said he felt uncomfortable when people spoke other language on a train
9/12 When he said the British army should be deployed to France
At the height of trouble at Britain’s Calais border Mr Farage proposed a novel solution. The Ukip leader called for the British army to be sent to France to put down a migrant rebellion. “In all civil emergencies like this we have an army, we have a bit of a Territorial Army as well and we have a very, very overburdened police force and border agency,” he said. “If in a crisis to make sure we’ve actually got the manpower to check lorries coming in, to stop people illegally coming to Britain, if in those circumstances we can use the army or other forces then why not”
10/12 When he said breastfeeding women should ‘sit in the corner’
Mr Farage sparked protests from mothers after he told women to “sit on the corner” if they wanted to breastfeed their children. “I think that given that some people feel very embarrassed by it, it isn’t too difficult to breastfeed a baby in a way that's not openly ostentatious,” Mr Farage said. He added: "Or perhaps sit in the corner, or whatever it might be”
11/12 When he said the gender pay gap exists because women are ‘worth less’
At a Q&A on the European Union in January 2014 Mr Farage said there was no discrimination against women causing the gender pay gap. Instead, he said, women were paid less because they were simply “worth far less” than many of their male counterparts. “A woman who has a client base, has a child and takes two or three years off - she is worth far less to her employer when she comes back than when she went away because that client base won't be stuck as rigidly to her portfolio,” he said
12/12 When he said he actually couldn’t guarantee £350m to the NHS after Brexit
During the EU referendum campaign the Leave side pledged to spend £350 million a week on the National Health Service – claiming that this is what the UK sends to Brussels. Nigel Farage didn’t speak out against this figure and also pledged to spend EU cash on the health service and other public services himself. Then the day of the election result he suddenly changed his tone, saying he couldn’t guarantee the cash for the NHS and that to pledge to do so was “a mistake”
She saw off a challenge from local politician Lisa Duffy after other contenders Mr Woolfe and Ms Evans were ruled out.
During the leadership battle she promised to focus on Brexit negotiations but consistently refused to set out any policies, insisting she did not want to make it "on the hoof".
Party insiders suggested she had been pushed into standing and she also refused to take part in any of the leadership hustings, only taking questions at her own campaign events.
Then on Monday, the Electoral Commission confirmed that it was yet to receive paperwork from Ukip confirming Ms James was the party’s new leader.
It was reported that Ms James did sign the forms but added the words “under duress” in Latin underneath her signature, rendering it void.
One Ukip source said that it technically meant Mr Farage was still leader, but one journalist said the ex-leader told him he wouldn't return "for $10 million", adding: "No I'm not coming back, I'm retired".
But a Ukip insider said: “He may come back. He’s done it before. Don't rule it out”
Mr Farage first became leader in 2006 and led the party to second position in the 2009 European Parliament elections. He then stepped down to contest the 2010 general election, but came third in the Buckingham constituency, only to go on and win a Ukip leadership contest in November of that year and return to his party's top job.
He again announced his resignation as leader after losing in South Thanet in last year's general election, but his resignation was rejected and he remained in post, leading to accusations that he had quit and then ‘un-resigned’.
His return prompted bitter infighting that saw several of his rivals demoted or sacked. After Ukip's EU referendum victory Mr Farage resigned again saying he wanted his "life back".Reuse content