He has previously said the odds of a no-deal Brexit were "a million to one".
UK Prime Minister Boris Johnson said he would hold new discussions with the European Union on Brexit but stressed that the Irish backstop "had to come out".
Speaking to reporters at a press conference at the end of the G7 summit in Biarritz, Johnson also said the EU was a tough negotiator but added that that didn't mean he won't try to reach a deal.
When asked by Reuters if he was prepared to take talks with the EU right up to October 31, Johnson answered that the bloc did tend to reach agreements at the 11th hour.
"Clearly for us, the walking away as it were, would come on October 31 when we would take steps to come out on the terms for which we will have by then made absolutely colossal and extensive and fantastic preparations."
The British prime minister added that in case of a no-deal, "substantial sums from €39 billion Brexit bill" would be made available to the UK to spend domestically.
Johnson also made clear he was not looking for a "quick trade deal" with the US but rather a "comprehensive one".
Earlier Johnson said the chances of a Brexit deal are "touch and go" in interviews with British media on the sidelines of the G7 summit.
He has previously said the odds of a no-deal Brexit were "a million to one".
"Let me give you a metaphor," Johnson told ITV. "I swam round that rock this morning. From here you cannot tell there is a gigantic hole in that rock. There is a way through."
"My point to the EU is that there is a way through, but you can't find the way through if you just sit on the beach."
It came after US President Donald Trump told Johnson on Sunday morning that Brexit Britain will have a major trade deal with the United States before saying that the new British prime minister was the right man to take his country out of the EU.
Read more: What is the G7? A look at the economic summit coming to France this month
The pair met for their first bilateral meeting at the G7 summit in France, with Johnson saying he had made clear the UK's National Health Service (NHS) was off the table in trade talks with the US.
The new leader is walking the tightrope at the gathering, trying to keep European allies on side, whilst not angering Trump — he said trade talks with the United States would be tough but there were huge opportunities for British businesses in the US market.
The new UK leader was set to meet European Council head Donald Tusk on Sunday morning — the pair clashed on Saturday over who would be to blame in the case of a no-deal Brexit.
Tusk said Johnson was at risk of being known as "Mr No Deal" but the prime minister responded by saying it was Tusk who would become "Mr No-Deal Brexit".
Johnson said upon his arrival in Biarritz on Saturday that he would be telling Trump to pull back from the US-China trade war that is already destabilising economic growth around the world.
Speaking to reporters, the British leader said one of his priorities for the summit was "clearly the state of global trade. I am very worried about the way it's going, the growth of protectionism, of tariffs that we're seeing".
"Don't forget that the UK is at risk of being implicated in this," Johnson said. "This is not the way to proceed. Apart from everything else, those who support the tariffs are at risk of incurring the blame for the downturn in the global economy, irrespective of whether or not that is true.
"I want to see an opening up of global trade, I want to see a dialling down of tensions and I want to see tariffs come off."
A surprise visit from Zarif
The Iranian Foreign Minister Javad Zarif landed in Biarritz in a surprise move. He met with French President Emmanuel Macron and French foreign minister Jean-Yves Le Drian.
Macron also held talks with Iranian Foreign Minister Mohammad Javad Zarif in Paris on Friday, ahead of the G7.
Euronews' Anelise Borges spoke to Zarif about his discussion with the French leader: "We discussed with Macron how the US could come back, and how Europe and the international community can live up to their commitments, independent of the US," he said.
Read more: Iranian foreign minister tells Euronews about his discussion with Macron
US-China trade war
On Friday, Beijing announced it would raise tariffs on US goods worth around €68 billion.
A retaliatory measure was taken in response to Washington imposing additional €270 billion tariffs on Chinese goods, set to come into effect from September and mid-December.
US President Donald Trump responded to China on Twitter saying that the vast amounts of money made and stolen by China from the United States, year after year, for decades, will and must stop.
Trump also ordered American companies to immediately begin the search for alternative trading options to China; be it relocating companies or relocating production to the US.
This is the latest episode in the long-running trade war between the two richest countries with repercussions being felt worldwide. Both the World Bank and International Monetary Fund have lowered their economic growth forecast for this year. They now predict it will between 2.6 and 3.2%.
On Sunday morning at the G7, Trump said he was not concerned about the market reaction to the spat, which stoked market fears that the global economy will tip into recession and sent US stocks into a tailspin.
When asked if he was having second thoughts, he said: "I have second thoughts about everything."
"We are very close to a trade deal with Japan," he said, adding the situation with China was helping this process.
G7 summit to be 'a difficult test of unity,' says Tusk
The summit in Biarritz will prove "a difficult test of unity and solidarity" after a year during which leaders of the rich nations have struggled to find a common language, European Council President Donald Tusk said in his opening statement.
He added that trade wars among the G7 members would serve to further erode trust among them.
Under no condition can the EU agree with a Trump proposal to bring Russia back into the G7 after it was excluded for annexing Crimea and backing an anti-Kyiv rebellion in eastern Ukraine, Tusk said.
On the topic of Brexit, Tusk said the EU was always open to cooperation before now to avoid Brexit and a no-deal scenario, but added the one thing the bloc would not cooperate on was a no-deal. Boris Johnson will not want to go down in history "Mr No Deal", the leader added.
'So far so good,' says Trump on arrival
Trump seemed positive upon arriving in Biarritz, saying: "We'll accomplish a lot this weekend."
"So far so good," he said of the three-day summit, adding that he had a special relationship with French counterpart Emmanuel Macron.
Sitting on a terrace with the French president, Trump said of their relationship: "We actually have a lot in common, Emmanuel and I. We have been friends for a long time. Every once in a while we go at it a little bit, not very much."
Also on the agenda, if French President Emmanuel Macron and UK Prime Minister have their way, are the wildfires sweeping the Amazon rainforest.
Macron called on members of the G7 to discuss the raging wildfires ravaging the Amazon rainforest in Brazil.
"Our house is burning. Literally. The Amazon rain forest - the lungs which produce 20% of our planet’s oxygen - is on fire. It is an international crisis. Members of the G7 Summit, let's discuss this emergency first order in two days! #ActForTheAmazon," the president tweeted on Thursday, a few days before the start of the G7 summit in Biarritz.
Read more: 'Our house is burning': Macron urges G7 leaders to discuss Amazon fire
His sentiment was backed up by Britain's prime minister Boris Johnson, who said he would use the G7 summit to call for a renewed focus on protecting nature, his office said on Friday.
“The prime minister is deeply concerned by the increase in fires in the Amazon rainforest and the impact of the tragic loss of these precious habitats,” said a spokeswoman.
World economic inequality
The gap between rich and poor in the majority of the G7 countries isn’t reducing. Combined, US, Canada, Germany, France, UK, Italy and Japan's populations, own more than half of total global wealth.
Of these countries, the richest 10% own approximately half or more of the country’s wealth, whilst the poorest 50% own 10% or less.
And with the world’s economy slowing down, this inequality gap won't be diminished any time soon.
Food for thought
Macron opened the summit with a dinner at the base of a clifftop lighthouse overlooking Biarritz, at which a menu of piperade, a Basque vegetable speciality, tuna and French cheeses awaited the leaders, Reuters reported.