Nigel Farage says he will demand his Brexit Party becomes part of the UK's negotiating team if it is successful in the forthcoming European elections.
The former Ukip leader branded Theresa May's proposed Brexit deal, which has already suffered three defeats in Parliament, a "new European treaty".
On BBC One's Andrew Marr Show, Mr Farage said: "What I do want to see from this European election, if we can win these elections, absolutely I'm going to demand that Brexit Party MEPs become part of the Government negotiating team and we can perhaps talk some sense into them."
Asked why he did not advocate a no-deal Brexit at the time of the EU referendum in 2016, he claimed it was "because it was obvious that we could do a free trade deal" - and blamed Mrs May for "the mess that we're in".
Mr Farage reacted angrily to being questioned about his controversial past comments on NHS privatisation, climate change, gun control, immigration and Vladimir Putin.
"All you want to do is go back to stuff from years ago, why don't we talk about now in British politics?" he said. "I think you're all in for a bigger surprise on Thursday than you can even imagine."
He said of Mrs May: "What she's put to Parliament isn't a deal, it's a new European treaty. I didn't spend 25 years campaigning to leave the EU to sign up to a new treaty.
"The only way we can deliver the democratic will of the people is to leave on WTO terms, and … once we do that the EU will be banging our door down to have a sensible tariff-free deal.
"This is our chance to break free of a failing political project to open ourselves up to the rest of the world, to get some self-confidence back.
"If we had a second referendum, I think Leave would win by a bigger margin," he added.
Mr Farage also admitted he is "mentally preparing myself for one, adding: "I'm thinking we may well have it forced upon us."