- Video report by ITV News Correspondent Daniel Hewitt
Boris Johnson says the onus is on Europe to compromise on Brexit and the thorny issue of the Irish backstop.
He told ITV News: "Unless we are determined to come out on those terms [no deal], if we have to - and it's up to the EU, this is their call, if they want us to do this - unless we are determined to do it, they won't take us seriously in the course of the negotiations.
"It's absolutely vital that we are able to walk away."
Mr Johnson also insisted that should the UK leave without a deal, then farmers would be looked after.
He said - contrary to reports the agriculture industry would be decimated - that "the people of this country are full of resolve and purpose and we will look after the farming sector".
"We will make sure they have the support that they need. If there are markets that are going to be tricky, that we help them to find new markets, that we have interventions that are aimed to support them and their incomes," he said.
Mr Johnson was also greeted with boos from protesters earlier when he arrived in Cardiff Bay to meet with First Minister Mark Drakeford.
The prime minister hit back at comments made by Wales's First Minister Mark Drakeford that a no-deal exit would be "catastrophic" for the Welsh economy.
He also pleaded with Leave-supporting voters not to back the Brexit Party in a crunch by-election.
The Prime Minister faces having his majority cut to just one if the Conservatives fail to hold on to Brecon and Radnorshire.
Ex-MP Chris Davies lost the seat after being ousted by constituents following his conviction for submitting fake expenses invoices.
The Tories have backed Mr Davies to fight the seat again despite his conviction and Mr Johnson is to visit the constituency during his first trip to Wales as Prime Minister.
He said: "The Brexit Party cannot deliver Brexit, only the Conservatives can."
The Liberal Democrats are hopeful of regaining a constituency they held until 2015 and have been boosted by Plaid Cymru's decision not to field a candidate in order to avoid splitting the pro-EU vote.
But Mr Johnson said the Lib Dems "will do everything they can to stop Brexit" so "if the people of Brecon and Radnorshire want to get Brexit delivered on time, they need to vote for my candidate, Conservative Chris Davies".
During his visit to Wales, Mr Johnson faced a difficult meeting with First Minister Mark Drakeford who said earlier that he would give him a "very clear message" that "Brexit will be catastrophic for Wales".
He said: "It will decimate our agricultural and manufacturing sectors and risks ripping the union apart.
"The PM must stop playing fast and loose with our country."
Mr Johnson was using the visit to highlight support for farmers, claiming they will be boosted by leaving the EU's common agricultural policy and by the UK signing new trade deals.
"I will always back Britain's great farmers and as we leave the EU we need to make sure that Brexit works for them," Mr Johnson said.
"That means scrapping the common agricultural policy and signing new trade deals - our amazing food and farming sector will be ready and waiting to continue selling ever more, not just here but around the world.
"Once we leave the EU on October 31, we will have a historic opportunity to introduce new schemes to support farming - and we will make sure that farmers get a better deal.
"Brexit presents enormous opportunities for our country and it's time we looked to the future with pride and optimism."
Welsh Secretary Alun Cairns has suggested new global markets, including in Japan, will be available to sheep producers after Brexit.
In the event of a no-deal, there could be tariffs of around 40% on lamb and sheep meat exports to EU markets if the UK ends up trading with the bloc World Trade Organisation (WTO) terms.
The Prime Minister's visit follows his trip to Scotland on Monday, and comes after the pound fell to a two-year low against the US dollar amid fears a no-deal Brexit is becoming increasingly likely.
Sterling was down 1.24% to $1.2228 by the close of European markets on Monday.
The pound was also down against the euro by 1.34% to 1.0981.
The sharpening of the tone on no-deal has drawn criticism from some of the Prime Minister’s Conservative colleagues.
Scottish Tory leader Ruth Davidson met Mr Johnson in Edinburgh on Monday and expressed her opposition to a no-deal Brexit.
Meanwhile, former work and pensions minister Baroness Altmann has claimed a group of Tory peers are prepared to resign the whip if Mr Johnson’s Government pursues a no-deal Brexit.
Baroness Altmann, the former director-general of insurance firm Saga, told the BBC’s Newsnight: “We have to do whatever we can.
“I will not stand for leaving without a deal or continuing to threaten this irresponsible nonsense about it being fine if we lose all our free trade at a stroke.
“I don’t want to bring down the Government, I’m hoping that the Government will recognise through the summer that this strategy is flawed, that this has no democratic mandate, and that if we want to make a success of our future then we cannot possibly contemplate throwing away 40 years of integration – putting all our small businesses at risk, losing free trade not just with Europe but all the countries we have free trade with.”