Asked what impact it would have on Mrs May's keynote speech tomorrow, Mr Davis said: 'It's a different speech, she's the prime minister, she's got to give a serious speech about the future of not just Brexit but all the other elements of the domestic strategy - which of course Boris was talking about too.
"This is the moment to chuck Chequers", he said.
The minister, who described himself as a "stubborn optimist", also used his speech to call for unity in his party, which has been increasingly divided since Prime Minister Theresa May announced the "Chequers agreement" - a roadmap for the post-Brexit relationship between the United Kingdom and European Union - in July.
"And that means, instead of aping Corbyn, we have to take our basic Conservative ideas and fit them to the problems of today".
"We will give credence to those who cry betrayal and I am afraid we will make it more likely that the ultimate beneficiary of the Chequers deal will be the far right in the form of UKIP and therefore the far-left in the form of Jeremy Corbyn".
"We must show everyone in this country that we are that party", Mrs May will declare.
"I have no confidence in her delivering Brexit, but let's listen to the speech this afternoon".
Satirist Kaya Marr holds a painting mocking MP Boris Johnson outside the conference in Birmingham on Tuesday.
When pressed about Mr. Johnson's comments, she added: "There's one thing we all know about Boris is that he'll put on a good show".
"Surely to goodness we can take this Tony Benn tribute act and wallop it for six", he said, referring to the late Labour socialist cabinet minister.
USA and Canada agree free trade deal
It replaces the 24-year-old North American Free Trade Agreement , which President Donald Trump had called a job-killing disaster. Canada was left out when the US and Mexico reached an agreement last month to revamp the North American Free Trade Agreement.
Some of Johnson's supporters, while welcoming his speech, said they believed now was not the time to launch a leadership bid against May.
Duddridge then cemented himself firmly as a backer of Boris Johnson in an interview with Sky News, describing Johnson's Tuesday speech as "inspirational".
"Am I disappointed [that he didn't declare]?" "We need to support the Prime Minister, but we're out to change the policy".
"I want also to congratulate my friend Philip Hammond for predicting that I will never become prime minister, the first treasury forecast in a long time I think to have a distinct ring of truth", he said to prolonged laughter and applause.
Eurosceptic MPs led by former foreign minister Boris Johnson have held a string of packed fringe meetings to argue against May's plan for Britain to follow European Union trade rules on goods.
"We have a very, very strong leader in Scotland in Ruth Davidson who had a very significant contribution to make to this conference".
The wide-ranging speech was widely seen as Johnson's audition for May's job before the party faithful at their annual gathering.
Mr Johnson warned that voters would not forgive the party for "bottling Brexit".
"I think the whole country will be listening and the whole country will be saying here is a guy that was deeply involved in securing Brexit in the first place who is basically saying that Chequers is a constitutional outrage, and it is".