LONDON (Reuters) - Britain's UK Independence Party, whose growing influence helped prompt the calling of June's EU referendum, was plunged into turmoil on Wednesday over the choice of a new leader.

The favorite to replace Nigel Farage as leader has been excluded from the ballot for the contest after submitting his nomination papers late, the party's national executive committee (NEC) said.

Farage, among Britain's most outspoken and effective anti-EU campaigners, said last month he would stand down after having realized his ambition of winning the referendum in which Britons voted to leave the European Union.

On Sunday, a spokesman for Steven Woolfe, a UKIP MEP and the party's spokesman on migration and financial affairs, said he had submitted his application before the deadline but due to "technical problems" it had not gone through in time.

"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," the party said in a statement.

Woolfe said he was disappointed by the decision.

"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," he said in a statement.

Before the announcement, major UKIP donor Arron Banks said he would look to hold an emergency general meeting of the party to challenge the decision if Woolfe was blocked.

Among the six candidates who have made the ballot, UKIP MEP Diane James is now the bookmakers' favorite.

UKIP won 12.6 percent of the vote in last year's general election but under Britain's winner-takes-all system, it gained only one seat in parliament.

(Reporting by Kylie MacLellan; editing by Stephen Addison)