Nigel Farage has accused Theresa May of “wilfully deceiving” people over her negotiated EU deal.
The Brexit Party leader told the BBC’s Andrew Marr the PM’s proposed Brexit deal was a “new European treaty”.
In a tense interview, Mr Farage said he would demand his party became part of the government negotiating team if it was successful in the forthcoming European elections.
Elections to the European Parliament take place on 23 May.
Asked why he did not advocate a no-deal Brexit at the time of the EU referendum in 2016, Mr Farage said: “Because it was obvious that we could do a free trade deal.
“The problem is the prime minister never asked for it, so we finished up in the mess that we’re in,” he said.
“She chose to go for this close and special partnership. Basically right from the start she was happy for us to be kept very close to the customs union.
“So where we are now, the only way the democratic will of the people can be delivered is to leave on a WTO (World Trade Organization) deal.”
Mr Farage’s fellow guests on the Marr programme included Education Secretary Damian Hinds, who said the European Parliament elections would be seen by some people as a protest vote.
“For some people this is the ultimate protest vote opportunity. Actually, ironically this is, in a sense, for some people, this is the second referendum,” he said.
Mr Farage said he believed that if there was a second referendum, the campaign to leave the EU would win by a bigger margin.
He said he was “mentally preparing myself for one”, adding: “I’m thinking we may well have it forced upon us.”
The interview on the BBC programme also saw Mr Farage asked about past comments on NHS privatisation, climate change, gun control, immigration and Russian President Vladimir Putin.
Responding angrily, he said: “All you want to do is go back to stuff from years ago, why don’t we talk about now in British politics?
“I think you’re all in for a bigger surprise on Thursday [the EU elections] than you can even imagine.”
Lib Dem deputy leader Jo Swinson said Mr Farage had refused to “own up to well-documented and abhorrent views on NHS privatisation, his admiration for Vladimir Putin and his denial of the facts about climate change”.
She said: “Despite his claims to the contrary, everyone remembers that he promised in 2016 that there would be an amazing cost-free Brexit deal available to Britain if we voted to leave the EU.
“To say today that he always advocated ‘no deal’ is a mark of just how shameless he is, and how little he cares for the jobs and livelihoods of the people of this country.”