Ukip's Steven Woolfe has complained about being excluded from the leadership race to replace Nigel Farage - for submitting his nomination papers 17 minutes late.
Supporters claimed the party's migration spokesman had been the victim of a coup led by Ukip's only MP, Douglas Carswell, and Neil Hamilton, group leader in the Welsh Assembly.
The decision was made by the ruling National Executive Committee - which Woolfe slammed as "not fit for purpose".
Woolfe said: "I am extremely disappointed by the Ukip NEC decision to exclude me from the party's leadership election.
"Over the course of this leadership election, the NEC has proven it is not fit for purpose and it confirmed many members' fears that it is neither effective nor professional in the way it governs the party."
MEPs Bill Etheridge, Diane James and Jonathan Arnott will be on the ballot along with Elizabeth Jones, Councillor Lisa Duffy and Phillip Broughton.
A Ukip spokesman said: "By a clear majority of NEC members, Steven Woolfe MEP's application was considered to be ineligible as a result of a late submission and as such he did not meet the eligibility criteria. His membership of the party was not in question."
Three members of the NEC immediately resigned from the committee in protest over the "deliberate obstruction" of Woolfe's nomination.
Victoria Ayling, Michael McGough and MEP Raymond Finch said the "escalating megalomania" of members of the board had been "detrimental to the functioning of the party".
They added: "Rather than acting as servants of the party, many on the NEC are acting as the owners. The factionalism has seen some of the party's top talent and most loyal officers wilfully excluded."
"Steven Woolfe is a popular candidate among Ukip's members and should be permitted to represent those that wish to vote for him. To purposefully trawl for technicalities upon which to base a decision to deny his inclusion is not in the best interests of the membership and truly injurious to Ukip."
They called for an extraordinary general meeting to allow a vote of no confidence in the NEC.