Calling May's plan, also known as the Chequers Plan, a "cheat", Johnson said: "If we cheat the electorate (with the plan), we will escalate the sense of mistrust".
The Conservative party chief called for unity to deliver a Brexit that was in the "national interest", amid deepening divisions within the ruling party over the UK's exit strategy from the European Union (EU).
Some of Johnson's supporters, while welcoming his speech, said they believed now was not the time to launch a leadership bid against May. What we are proposing is very challenging for the EU. Instead choosing to focus on the Conservative domestic record in government, the speech was light on policy and announcements, announcing only a freeze in fuel duty, extra money for cancer treatment and extra borrowing for housebuilding.
Foreign secretaries Brexit talks between the United Kingdom and European Union have stalled in recent weeks with the issue of the Irish border remaining a stumbling block.
"We are entering the most hard phase of the negotiations", underlined the leader of the uk.
"If we all go off in different directions in pursuit of our own vision of the flawless Brexit, we risk ending up with no Brexit at all", she said, a rebuff to eurosceptic MPs who have published their alternatives plan for leaving the EU.
The former foreign secretary, with his colourful turn of phrase and humorous flourishes, can certainly hold an audience as he showed earlier this week but as a party leader he would be disastrous. May insists her ideas offer the only way to protect jobs and trade while also avoiding physical checks on Britain's land border with European Union member Ireland.
Kavanaugh a step closer to lifetime Supreme Court post after Senate vote
Steve Daines to stay at his daughter's wedding in his home state instead of flying to Washington to cast his supporting vote. It just may be that in my view he's not the right man for the court at this time", Murkowski told reporters on Capitol Hill.
"Emotional arguments that stress the issue of dignity sound attractive, but they do not facilitate agreement".
And, unlike past year, when the letters behind her spelling out "Building A Country That Works For Everyone" fell off the pinboard they were attached to - like a sputtering clown vehicle - the words "Opportunity" were, quite fittingly, spelt out on a digital screen.
In a nod to voters who are exhausted of stagnating wages and spending cuts, May said that from next year the government would end the austerity policies introduced after the 2008 global financial crisis and put more money into public services.
After a decade of austerity that has seen public sector pay restraint and real terms funding cuts for many public services, May said that national debt is beginning to fall and "people need to know that their hard work has paid off". But she remains defiant.
Another Brexiteer who enjoyed a successful week from the fringe of the party conference. The Conservatives, in contrast, were full of doubt.
While anti-EU delegates railed against May's compromises and the iniquities of Brussels, pro-EU Tories claimed the departure had tainted the party with an inward-looking image that turns off voters, especially the young.
In a conference where the policy agenda put forward by Corbyn and his shadow Cabinet has received more comment than ever before, May will attack her opposite number's leadership call for a return to decency in political discourse.
Forty-eight legislators would need to write such letters to trigger a vote of confidence in the leader. No one knows yet how many have already submitted their requests.