Ukip leader Paul Nuttall has insisted the party is still "on the pitch" despite disastrous local election results which saw them shed more than 100 councillors and win only one seat.
The near-wipeout led Arron Banks, who formerly bankrolled the eurosceptic party, to declare it "finished as an electoral force" under its current leadership.
But Mr Nuttall predicted that voters would come back to Ukip "in their droves" once they saw Theresa May "backsliding" in Brexit negotiations following the June 8 General Election.
Campaigning in the Lincolnshire constituency of Boston and Skegness which he is hoping to seize for Ukip on June 8, Mr Nutall said: "Ukip does have a great future. It just has to stay on the pitch, hold its ground and people will come back to us."
Mrs May had called the snap election purely in order to get it under way before Brexit negotiations began in earnest, said Mr Nuttall.
"It is very easy for her to talk the talk and act tough, but when she's asked to walk the walk, I think there's going to be problems," he told the BBC.
"I think she will start to barter things away. I think fisheries will go, I think there will be some sort of movement on immigration and freedom of movement, I think she might buckle on that. And I think she will certainly buckle on the divorce bill.
"When people are angry, when people feel they have been let down, when people feel they aren't getting the Brexit they wanted and they voted for on June 23, where are they going to go?
"They are going to return to Ukip. The future of Ukip is very bright indeed."
After seeing Ukip lose all 10 of its councillors in its former stronghold of Lincolnshire on Thursday, Mr Nuttall acknowledged that he was "not the favourite" in Boston and Skegness, where he is challenging a 4,336-vote majority for Conservatives in the 2015 election.
But as he campaigned in the town of Burgh-le-Marsh, he insisted Ukip had a unique message for voters on its commitments to cut immigration and foreign aid spending and tackle "integration" issues like female genital mutilation, sharia courts and forced marriages.
He told Sky News: "We knew that these local elections were going to be the most difficult we've ever fought.
"Of course Theresa May performed a massive U-turn, called a General Election and made them doubly difficult for us.
"But we dust ourselves down and we go on."