A no-deal Brexit would endanger not only agriculture but rural life as a whole, the Welsh first minister has said.

Mark Drakeford said he took very seriously the risk of civil unrest in the countryside if farmers’ livelihoods were lost.

Speaking to the Guardian during Boris Johnson’s visit to Wales, Drakeford said: “It is a sector of the economy that has the capacity, if it feels sufficiently provoked, to carry out acts of civil disobedience.”

He said the Welsh countryside would be put under huge strain if there was no deal. “We’re not simply talking about an economy here. We’re talking about a whole way of life that has existed for centuries and which will be put at peril in a way that it has never been put at peril before.”

Mark Drakeford. Photograph: Matthew Horwood/Getty Images

Drakeford said the Labour-led Welsh government had been pointing out for months that no deal would be catastrophic.

“We are particularly exposed to some of the impacts of a no-deal Brexit,” he said. “Manufacturing is a larger percentage of our economy than any other part of the United Kingdom and tariffs in a no deal will place enormous barriers in the path of our manufacturing industry.”

Drakeford noted the sheep industry had attracted headlines in the last few days and he also cited the shellfish industry, which he said could crash within weeks of a no-deal departure from the EU. The vast bulk of Welsh shellfish goes to the southern Mediterranean.

“We have a very successful shellfish industry that has been built up over the last 20 years and more,” he said. “It leaves fresh, it arrives fresh, there are no impediments to trade. That 20-year investment could be over in three weeks in a no-deal Brexit. The product will not be saleable. It will not be fresh on arrival. You cannot create a home market for products on that scale in the few weeks we have between now and the end of October.”

Drakeford said the Welsh government would always try to be constructive with the UK government, but he added: “We will need more than bluff and bluster if we are to have a serious conversation about the deeply serious issues that face us both in terms of our relationship with the European Union but also in relation with the United Kingdom itself.

“I think the union that is the United Kingdom is more at risk today than at any time in my political lifetime. The Scottish government has a particular political project. Scotland voted heavily to remain in the European Union. There are inevitably tensions there. The north of Ireland voted to remain in the EU. A hardline Brexit in which the impact on the island of Ireland is swept away as if it is of no significance plays into all sorts of debates and different futures that could be possible in Ireland.

“The Welsh government believes that Wales’s future is best secured by a powerful devolution settlement but also we think Wales’s future is best secured in a successful United Kingdom. The United Kingdom is at risk.”

Drakeford said Johnson could either find a way of allowing the UK to reinvent itself or proceed in a manner that would exaggerate the fissures.

“There’s a lot of debate about democratic legitimacy and respecting referendums. There’s a democratic issue here for an incoming prime minister where no deal was never on any ballot paper and where in Scotland and Wales his party has not won a majority of seats in any form of election in living memory.

“The prime minister needs to think about the future of the United Kingdom in genuinely serious way. Just a few more choruses of Rule Britannia and an extra supply of union jacks is not going to cut it.”