Shrewsbury's Suzanne Evans back in the running to lead Ukip after Diane James resignation shock

The party has been thrown into disarray after Ms James's resignation last night.

Ms James cited "personal and professional" reasons for her decision, saying that she had not been given sufficient authority to force through changes she wanted to make to the party.

It is also thought that her husband's ill-health and a recent incident in which she was "badly shaken up" after being verbally abused and spat at in a central London street may have played a role in persuading her to step down.

Confusion surrounded her position after she suggested in a statement that she had never formally taken up the role of leader after winning a landslide victory in the race to succeed Nigel Farage on September 16.

Party sources questioned her claim that the election amounted only to a "nomination" as leader which needed to be registered with the Electoral Commission to be formally confirmed.

Ukip's ruling National Executive Committee is expected to hold an emergency meeting within days to choose an interim leader and agree a timetable for the second leadership election within weeks.

Bookmakers installed North-West England MEP Steven Woolfe - who was barred from standing to replace Mr Farage after handing nomination papers in 17 minutes late - as hot favourite, followed by Suzanne Evans, who stood for Ukip in Shrewsbury during the general election but missed out on the chance to run for leader because of a suspension which has now been lifted.

Ms Evans is 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.

In Ms James's brief time as leader, she had not appointed a deputy. In the interim Nigel Farage today announced he would continue as "acting Ukip leader" but ruled out standing as a candidate for his old job.

Mr Farage poured cold water on speculation he might return to lead the party for a third time, after stints from 2006-09 and 2010-16, telling the Press Association: "Not for 10 million dollars."

And asked if he would take 20 million dollars, he said: "No, I'm not coming back, I'm retired."

Ukip chairman Paul Oakden said on Tuesday: "It is with regret that I have tonight 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."

It is understood that Mr Oakden was not informed in advance of Ms James's intention to quit, and received formal confirmation only when she released a statement on Twitter.

In a statement announcing her decision, 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 insiders questioned suggestions that Ms James had failed to receive support from officials.

The 56-year-old former Conservative councillor, who defected to Ukip in 2011, said she would stay on as an MEP for South-East England.

Elected to the European Parliament in 2014 after achieving national prominence as second-placed candidate in the 2014 Eastleigh by-election, Ms James was the party's first woman leader and won the post by a wide margin after winning the backing of senior Ukip figures including Mr Farage.

But questions were raised about her commitment to the post after she declined to take part in hustings debates around the country with rival candidates.

In September's election, Ms James took 8,451 out of the 17,970 votes cast, romping home ahead of Lisa Duffy - backed by many in the anti-Farage wing of the party - Bill Etheridge, Phillip Broughton and Elizabeth Jones.

In her acceptance speech, she promised to bring a new professionalism to the party, saying: "We are going to confound our critics, we are going to outwit our opponents, we are going to build on our election success that we have achieved to date and do more."

Ukip's only MP, Douglas Carswell, declined to comment on Ms James's resignation, saying in a tweet: "In the middle of supper. Not taking calls about UKIP stuff. It's shepherds pie, by the way."

Who else could be in the running to replace Diane James as leader of Ukip?

No-one has yet throw their hat into the ring, but these are some of the other 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 Britain 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.

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.

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.

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''.