The prime minister is set to ramp up pressure on the post-Brexit trade talks as he will say there is "no sense" in continuing negotiations if an agreement cannot be reached by his mid-October deadline.
The intervention comes after months of deadlock between EU and UK negotiators over the terms of the future relationship between the two sides once the Brexit transition period ends in December.
But Johnson will say today that unless there is a breakthrough by October 15 then he is willing to "move on" from the talks and accept a no-deal outcome. It comes amid reports that ministers are drawing up new legislation which would override key parts of the Brexit withdrawal agreement.
"We are now entering the final phase of our negotiations with the EU. The EU have been very clear about the timetable. I am too," he will say.
"There needs to be an agreement with our European friends by the time of the European Council on October 15 if it's going to be in force by the end of the year.
"So there is no sense in thinking about timelines that go beyond that point. If we can't agree by then, then I do not see that there will be a free trade agreement between us, and we should both accept that and move on."
And the PM said if no deal was reached then the UK would prepare to trade with the EU on the same terms as Australia, which does not have a free-trade agreement with the bloc.
"We have said right from the start that would be a good outcome for the UK," he will say.
"As a government we are preparing, at our borders and at our ports, to be ready for it.
"We will have full control over our laws, our rules and our fishing waters. We will have the freedom to do trade deals with every country in the world. And we will prosper mightily as a result."
An eighth round of formal negotiations are set to begin on Tuesday, with talks focussed on the key sticking points of fishing rights and state aid rules, which control the level of taxpayer support the UK government can offer to British businesses.
Speaking ahead of the talks, EU negotiatior Michel Barnier said he was "worried and disappointed" in the UK's refusal to offer concessions during previous rounds.
But the talks are likely to come under further pressure following reports that ministers were drawing up new legislation which would circumvent key parts of the Brexit withdrawal agreement.
According to the Financial Times, sections of the internal market bill, set to be published on Wednesday, will "eliminate the legal force of parts of the withdrawal agreement", including around state aid rules and the Northern Ireland protocol which was signed last year to ensure there would not be a hard border on the island of Ireland.
One source told the paper the plan was a "very blunt instrument".
They added: "The bill will explicitly say the government reserves the right to set its own regime, directly setting up UK law in opposition with obligations under the withdrawal agreement, and in full cognisance that this will break international law."
But the reports drew anger from Labour, who said Johnson's threat to "renege on the UK's legal obligations" would be "an act of immense bad faith: one that would be viewed dimly by future trading partners and allies around the world".
Labour's shadow Northern Ireland secretary Louise Haigh said: "It beggars belief the government is - yet again - playing a dangerous game in Nothern Ireland and sacrificing our international standing at teh altar of the Prime Minister's incompetence."
Meanwhile, Ireland's foreign affairs minister, Simon Coveney, said the plan would be a "very unwise way to proceed".
Responding to the reports, a government spokesperson told the paper they were "working hard to resolve outstanding issues" around the Northern Ireland protocil.
They added: "As a responsbile government, we are considering fallback options in the event this is not achieved to ensure the communities of Norther Ireland are protected."