Former Ukip leader Diane James has announced she is quitting the party.
James was elected successor to Nigel Farage in September, but she remained in the post for just 18 days before announcing she was standing down.
In a statement, she said she had applied to become an independent MEP in the European Parliament and that her relationship with Ukip had become "increasingly difficult" since her decision not to take up the leadership.
James said her decision not to serve as leader was prompted by the fact she had received "no support within the executive" of the party.
Elected a Ukip MEP for South-East England in 2014, she has now requested to be allowed immediately to take up the status of an independent in the European Parliament.
In a statement, she said: "The President of the Parliament, Martin Schulz, has accepted my request and will announce this in his opening speech to the parliamentary session in Strasbourg on Monday November 21.
"At a high profile public event in Cambridge last week, I was asked why I had not completed the process to become leader of Ukip.
"I had little option but to give the truthful response that, although nominated leader by popular vote in the membership, I found that I had no support within the executive and thus no ability to carry forward the policies on which I had campaigned.
"My decision to retire from the election process and not complete it was very difficult personally and professionally, given that Ukip has dominated my life and all my efforts for over five years.
"In recent weeks, my relationship with the party has been increasingly difficult and I feel it is now time to move on. I wish the party well for the future under new leadership."
James, 56, said she would continue to serve constituents "effectively and diligently" as an independent for the remainder of her five-year term.
Ukip is currently undergoing its second leadership contest in a matter of months, with Paul Nuttall, Suzanne Evans and John Rees-Evans competing for votes of party members, with the successor to Farage due to be announced on November 28.
James's departure means that the 24-strong contingent of Ukip MEPs elected in 2014 has been reduced to 20. Amjad Bashir defected to Conservatives in 2015, while Steven Woolfe and Janice Atkinson now sit as Independents.
I am very sorry to hear Diane James has... - Suzanne Evans UKIP | Facebook
Evans said that all four - including James - should give up their seats, which they secured due to their position on Ukip party lists under a proportional representation system.
"I am very sorry to hear Diane James has decided to leave Ukip," said Evans. "I am sure she has her own personal reasons and I do not question those.
"However she, like Steven Woolfe, were both elected as MEPs on a Ukip ticket, not as individuals. If they have any honour or integrity, both should now stand down as MEPs and vacate their seats. I reiterate my call for defectors Amjad Bashir and Janice Atkinson to do the same, for the same reasons."
Ukip MEP Patrick O'Flynn said: "Sorry to lose a colleague but glad of my judgment that neither she nor Mr Woolfe were suitable candidates for leader."