One of the two candidates for the leadership has indirectly accused his rival of putting "self-preservation" ahead of party interests.
Bill Etheridge, an MEP, told this website that fellow candidate Diane James "should get her priorities right."
Etheridge is going head to head against another MEP, Diane James, the party's deputy Chair.
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James is the bookies' clear favourite to become new leader at the Ukip conference later this month. She has reportedly decided to boycott the official leadership hustings, instead running her own series of events.
Interviewed recently BBC Radio 4's Today programme, she argued there was "no need to debate with my rivals." She said: "What I'm doing is appealing direct to the members and activists."
But Etheridge has accused her of not being "focused" on Brexit after she called for Ukip to select candidates for the European elections in 2019.
He said, "Her priorities seem to be all wrong. Instead of assisting the fight for delivering Brexit, she is talking about 2019 and the Euroopean elections. She is putting internal politics ahead of the people and what they voted for in the EU referendum."
He added, "The people should come before self-preservation and I wish to state that my focus is fixed on continuing to put the squeeze on the government to deliver Brexit as a matter of urgency."
With neither candidate enjoying a national profile, there is speculation that Farage could yet return as leader, depending on progress in the Brexit negotiations.
James was not available for comment but, speaking to the UK national press recently, she denied Ukip was politically defunct after Britain voted to leave the EU, robbing the party of its central campaigning issue.
James said: "My biggest test will be to take the party out of Nigel's shadow and into the future.
"Ukip still has a job to do. We need to ensure that Theresa May triggers article 50 as soon as possible to send a clear message to Brussels that we are serious about Brexit."
The result of the contest is expected on 15 September. Ukip was the UK's third-biggest political party by vote-count in the 2015 general election.