Video report by ITV News Correspondent Angus Walker
Nigel Farage has urged Boris Johnson to form a "Leave alliance" - or face opposition in every seat from the Brexit Party.
Speaking to ITV News, Mr Farage urged the prime minister to ditch his deal with Brussels or risk facing the Brexit Party in "every seat across England, Scotland and Wales".
Mr Farage said the deal Mr Johnson had negotiated would be the "death of Brexit".
"We've got a chance here in a general election to press the reset button. That's what general elections are about. They're about fresh starts," he told ITV News Correspondent Angus Walker.
"Most of his own members want it, most of his own voters want it, huge numbers of people around the country just want us to have a proper Brexit, so it's a big opportunity.
"If he doesn't do it, it's a historic mistake."
Mr Farage revealed his offer to Mr Johnson would see the Brexit Party stand in seats the Conservatives had little chance of winning, and in return, the Brexit Party would stand in Labour strongholds which voted to Leave.
He said: "I'm talking about a non-aggression pact. We would fight seats the Conservative Party had never won in their entire history and stand aside for them in very large areas of the country.
"I mean, I'm being very generous about this. I want to put country before party. But if he's not prepared to do that, then we will stand in every seat."
Johnson's deal would be 'the death of Brexit'
The Brexit Party leader was highly critical of Mr Johnson's newly negotiated deal during the launch of his party's general election campaign.
He told Angus Walker: "The government is not offering Brexit. It's offering Brexit in name only. It's an inferior form of membership. It's so bad that if we go down this route, we'll undoubtedly rejoin."The Brexit deal on the table will be the death of Brexit. It takes us to a place that's far worse than being a member, and will lead to us rejoining. Let's drop the deal, let's go for a proper Brexit."
Speaking at the The Brexit Party's launch, Mr Farage said he was "flexible" in his negotiations with the Conservative Party but warned that his offer would only last two weeks.
If they refused his offer, the Conservatives would face competition in 500 seats across the country, which could weaken the Tories' chances of a majority and getting their Brexit deal over the line.
Mr Farage claimed he had talked to a number of MPs who were ready to ditch Mr Johnson's deal in favour of a free trade agreement with Brussels.
The Brexit Party leader confirmed no formal talks had been held between himself and the Conservative hierarchy, but warned the prime minister there were MPs ready to "stand on a ticket of a genuine free trade agreement or leave on WTO terms".
Mr Farage said: "And of course in those cases where MPs say this, we will view them as our friends and not as our enemies.
"But that is not the real deal. The real deal is a Leave alliance that wins a big majority in Parliament. The real deal is a Leave alliance that delivers a genuine Brexit."
Asked why people should vote for the Brexit Party, Mr Farage said: "Because we stand for Brexit. And at the moment we're the only party in England, Scotland and Wales that believes in Brexit.
"Brexit is about us becoming an independent country - being free, being able to make our own decisions, not under the rule book of the European Union.
"The problem with Boris's new EU treaty is that it keeps us tied to EU rules, costs us a fortune, but what it really does is kick the can down the road for a further three years of agonising negotiations.
"It's simply not Brexit. So what I'm saying is - it's a general election, it's a chance to press the reset button, drop the deal and let's move forward and let's form some kind of Brexit alliance and win the election."
Trump tells Farage he's no fan of Johnson's Brexit deal
The Brexit Party leader echoed the sentiment of Donald Trump during his appeal to Mr Johnson on Friday, claiming the deal with Brussels was a "sell out" of what Brexit represented.
During a phone-in to Mr Farage's LBC radio show on Thursday evening, Mr Trump said he was a fan of Mr Johnson but that the deal had limitations when it came to trade with the US.
The US President told Farage: "We want to do trade with UK and they want to do trade with us," he said.
"To be honest with you... this deal... under certain aspects of the deal... you can't do it, you can't do it, you can't trade.
"We can't make a trade deal with the UK because I think we can do many times the numbers that we're doing right now and certainly much bigger numbers than you are doing under the European Union."
The US president also urged the prime minister and the Brexit party leader to "get together", describing them as "two brilliant people" who would make an "unstoppable force", in what appeared to be a call for them to form a pact.
However a Number 10 source fired back, insisting Mr Johnson's deal would allow Britain to "take back control" from the EU.
They said: "The PM negotiated a new deal which ensures that we take back control of our laws, trade, borders and money - a deal which people said he could never negotiate.
"Under this new deal the whole of the UK will leave the EU Customs Union, which means we can strike our own free trade deals around the world from which every part of the UK will benefit.
"This election will allow voters to choose a Parliament actually willing to get Brexit done so this country to move on – all Jeremy Corbyn can offer is two referendums next year and no leadership to take this country forward.”