Nigel Farage said he will serve as interim Ukip leader following Diane James' sensational resignation last night - just 18 days after winning the race to succeed him.

Party sources said the 51-year-old had been 'deeply unhappy' in her new role and had given up because of personal reasons.

Reports suggest she was 'shaken' after being spat at on a train on her way to Cardiff last week, and did not feel she had assurances from some members of her party.

Bookies immediately installed Mr Farage at 10-1 to make an extraordinary return to the helm of the Eurosceptic party that has been riven by infighting since the referendum.

Mr Farage confirmed today that he is technically still Ukip leader as Mrs James never completed the necessary paperwork to take over the post.

He promised the party he will 'continue as the interim leader of UKIP' until it elects a new leader and 'move forward,' but categorically ruled out standing in the upcoming contest, insisting: 'I've done my bit.'

Scroll down for video

Diane James has sensationally quit as Ukip leader tonight just 18 days after winning the race to succeed Nigel Farage. Party sources said the 51-year-old had been 'deeply unhappy' in the role

Bookies immediately installed Mr Farage at 10-1 to make an extraordinary return to the helm of the Eurosceptic party but he said tonight that he would not return for 'ten million dollars'

The elections watchdog told MailOnline that he is still listed as leader on its system because Ms James had failed to fill out her official leadership papers correctly.

The Electoral Commission also said the South East England MEP had missed the 14-day deadline for submitting her papers after being named the new Ukip leader at the party's conference in Bournemouth 18 days ago.

Steven Woolfe - who was left out of the summer contest after failing to submit his membership papers on time - is the early favourite to win the upcoming leadership election and confirmed today that he will be standing in the contest.

Ms James took over Ukip less than three weeks ago with a promise to 'wipe the slate clean' after a summer of bitter rows.

She was seen as Mr Farage's pick for the post after he resigned on the back of Brexit success - insisting he wanted to get his 'life back' after decades hammering at the political establishment.

But insiders claim Mrs James never really wanted the role and when signed her official declaration with V.C., signifying Vi coactus the Latin term for under duress.

Contenders for the leadership were today jostling for position as Mr Farage tried to rule himself out of the job.

Nigel Farage promised the party he will 'continue as the interim leader of UKIP' until it elects a new leader and 'move forward,' but categorically ruled out standing in the upcoming contest, insisting: 'I've done my bit.' Sky News captioned Mr Farage as 'Ukip leader (we think)' as it reported on the party's chaos this morning

Lisa Duffy, an obscure councillor who finished a distant second to Mrs James in the last contest, told the BBC: 'I didn't believe this was something that she particularly wanted to do or had the passion to do. So I'm not surprised.'

Ms Duffy said she would not rule herself out from running in another leadership election.

Ukip MEP Bill Etheridge said he was 'very disappointed' the leader had stepped down, describing her statement as 'peculiar'.

The MEP told ITV's Good Morning Britain: 'Unfortunately, Diane has stood down and the reasons for that are pretty unclear to me.'

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 Statement from Diane James

He added: 'She won the election fair and square and we were all ready to back her.'

Mr Etheridge, a runner-up in the leadership race, added that he would not rule out standing again for leader.

Suzanne Evans, a senior Ukip spokeswoman who was barred from the summer contest, last night told MailOnline she had not yet decided whether to run.

Ukip chiefs held crisis talks with her in attempt to persuade her not to stand down. But she is said to have insisted because of her unhappiness in the role and personal issues including the illness of her partner.

Ms James, who had dinner with Mr Farage in Strasbourg before announcing her resignation, reportedly felt 'shaken' after being spat at on a train on her way to Cardiff last week, The Times reported.

She is said to have been reluctant to continue leading the party without assurances about funding and had complained about Ukip's finances, the newspaper reported.

Diane James has sensationally quit as Ukip leader tonight just 18 days after winning the race

In a statement announcing her decision to step down, she 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. 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 election process further.

'I will continue to concentrate fully on my activities and responsibilities as an elected UKIP Member of the European Parliament for SE UK Region.'

The Electoral Commission told MailOnline: 'It is still listed on our system that Nigel Farage is leader.'

Steven Woolfe (right) - who was left out of the summer contest after failing to submit his membership papers on time - is the bookmakers' early favourite. Other candidates could be Suzanne Evans (left), barred from the summer contest, or Bill Etheridge who finished third

Confirming that Ms James had failed to correctly complete the necessary forms to officially become Ukip leader, a statement from the elections watchdog said this morning: 'The election and appointment of party leader's is a matter for the party, in line with their rules and constitution.

'After appointing a new leader, parties must notify the Commission within 14 days of the change in order that the statutory register can be updated.'

'UKIP submitted paperwork to the Commission notifying us of a change in their leadership on Monday 3 October, although this had not been processed as we had questions for the party regarding the completion of the form.

'We are aware that the newly elected leader of UKIP has now stood down and are in touch with the party to confirm how they wish to proceed regarding updating their entry on the statutory register.'

WHO IS IN THE RUNNING TO REPLACE THE UKIP LEADER? No-one has yet throw their hat into the ring, but these are some of the potential contenders. Nigel Farage Still a Ukip MEP and the party's best-known face, despite his decision to stand down as leader after the EU referendum. Mr Farage, 52, is known for changing his mind about the leadership, an office he has held twice, from 2006-09 and 2010-16. He tried to quit after missing out on a seat in Parliament in the 2015 election but his resignation was rejected after three days. Shortly after celebrating 'independence day' as Briton voted for Brexit, he stood down again, announcing 'I want my life back'. He was emphatic that he would not take another tilt at the job, telling the Press Association he would not do it 'for 10 million dollars'. But this did not stop bookies installing him as a 10-1 shot for the job. Steven Woolfe Barred from standing to succeed Mr Farage this summer after handing in his nomination papers 17 minutes late, the 48-year-old barrister was immediately installed as favourite to win the leadership this time round. Of mixed race and born and brought up in the North, Mr Woolfe is regarded by many within Ukip as a candidate able to broaden the party's appeal beyond its southern and middle-class core. Elected MEP for North-West England in 2014, he has been party spokesman in Brussels for migration and financial affairs. Nigel Farage (left) is the party's most familiar face but reckons he would not return even for $10million. Meanwhile, Steven Woolfe (right) has emerged as the bookmakers' favourite Suzanne Evans Widely seen as a good media performer who has burnished her reputation with numerous appearances on BBC1's Question Time, the 51-year-old former journalist was unable to stand in the summer's election because she had been suspended from the party over comments she made suggesting Mr Farage was a 'divisive' figure. Previously a Farage favourite, she was his choice as interim leader after his swiftly-retracted resignation in 2015. The suspension has since been lifted, clearing the way for a leadership bid. Deputy party chairman from 2014-16, she was responsible for writing much of the party's 2015 election manifesto. Paul Nuttall Ukip's former deputy leader and the current head of the party's delegation in the European Parliament. Many observers were surprised when the 39-year-old history lecturer announced he would not stand in the race to succeed Mr Farage. He is regarded as one of the potential candidates most likely to be able to capitalise on the high level of support for Leave among Labour's traditional working-class strongholds in the North. Paul Nuttall is the current head of the party's delegation in the European Parliament Douglas Carswell Ukip's only MP after sensationally defecting from the Conservatives in 2014 and being re-elected MP for Clacton in last year's general election. At odds with Mr Farage's anti-immigration stance, he fell out with the former leader soon after his arrival and was recently accused by Mr Farage of joining Ukip as part of a deliberate plot to split the party. Douglas Carswell (pictured) is Ukip's only MP after sensationally defecting from the Conservatives in 2014 and being re-elected Arron Banks The multi-millionaire 50-year-old businessman has bankrolled Ukip in recent years and was a prominent part of the Leave.EU campaign during the EU referendum, which pushed a much stronger line on immigration than the official Vote Leave organisation. Following the campaign, Mr Banks said that Leave.EU would continue campaigning as a 'right-wing Momentum' to ensure that politicians lived up to their promise to take Britain out of the EU, and he has also discussed forming a new political party. Lisa Duffy Former party director Lisa Duffy is chief of staff to Ukip MEP Patrick O'Flynn and had Ms Evans' support in this summer's election, in which she came second to Ms James with 4,591 votes, many drawn from the anti-Farage wing of the party. The ex-TK Maxx store manager wants a 'total ban' on Muslim schools but insists she is 'not far-right'. Advertisement

Earlier today, she was reportedly seen having a heated debate with fellow MEPs in a café at the European Parliament in Strasbourg. She is understood to have fled to her hotel room before later cancelling a planned speech in the chamber at the last minute.

The party's only MP Douglas Carswell insisted he knew nothing on Twitter and would not interrupt his dinner to find out.

After being contacted about the resignation, he said: 'In the middle of supper. Not taking calls about UKIP stuff. It's shepherds pie, by the way.'

He added to MailOnline: 'I'm both sad and surprised, I hope she's OK.'

In a further bizarre twist, it appeared Ms James may never have been officially installed as party leader by the election's watchdog.

Married 56-year-old Diane James waves as she is introduced at the UKIP Autumn Conference less than three weeks ago

Yesterday, the Electoral Commission confirmed to HuffPost UK it had not received the paperwork from Ukip confirming James was the party's new leader.

A spokesman said: 'We have been in contact with UKIP and are expecting the party's leadership change to be confirmed shortly.'

Confirming her resignation, UKIP Chairman Paul Oakden said: 'It is with regret that I have received confirmation that Diane James has chosen to resign as party leader, citing personal and other reasons.

'I will now look to convene an emergency meeting of our NEC to confirm the process for electing Diane's replacement.

'Whilst the decision is unfortunate, it is one that Diane is entitled to make. We thank her for all her work as leader, and as a hard working MEP, a role she will continue with her customary vigour'.

Ms James' early departure has raised speculation that her predecessor Mr Farage could make a return.

However, bookmakers have placed him at 10/1 odds to make a comeback, with Steven Woolfe - who was left out of the summer contest after failing to submit his membership papers on time - the early favourite. Other candidates could be Suzanne Evans, barred from the summer contest, or Bill Etheridge, who finished a distant third last time out.

Ms Evans confirmed that her suspension from Ukip had been lifted, clearing the way for her to enter any leadership race.

But she declined to say whether she was considering throwing her hat into the ring, telling PA: 'I think we all need to see what happens over the next few hours.'

She added: 'There is not a contest yet. I'm unable therefore to rule anything in or out.'

Earlier today party figures held crisis talks with Ms James in attempt to persuade her not to stand down. She is pictured alongside Nigel Farage after being appointed just 18 days ago

Nigel Farage made a triumphant final appearance as Ukip leader at Party conference on September 16 but tonight ruled out returning as party leader saying you 'couldn't pay him'

Ms James, an MEP, became the first woman to lead the Eurosceptic party when she won the contest to replace Mr Farage on September 16.

The front-runner throughout the leadership campaign, she was backed by supporters of Mr Farage and Ukip's millionaire funder Arron Banks.

Her landslide victory, which saw her gain 47 per cent of the vote, was made at the party's annual conference in Bournemouth just a fortnight ago.

It came after months of infighting between different factions divided by the tactics used in the referendum on the European Union.

Ms James had been criticised within the party for being too close to Mr Farage. But during her first speech as leader, she declared: 'I'm not Nigel-like, I'm not even Nigel-lite - and I will never, ever pretend to be so.'

She raised eyebrows last year in an interview where she had declared her admiration for the Russian president, saying that Vladimir Putin was 'a strong leader' who stands up for his country.

She began her leadership campaign by declaring there were no skeletons in her closet, but the Mail revealed she had been involved in the break-up of two marriages.

In 1998 a tabloid newspaper exposed her affair with senior MoD official Ron Smith, a married man and aide to then-Labour defence secretary George Robertson.

By 2005, Ms James, who attended Rochester Girls Grammar School, had taken up with another married man - John Forrest, who is 17 years her senior and had been married for 32 years at the time. The couple now live in a secluded £1million house in Surrey.