The new leader of the Welsh national party Plaid Cymru has declared himself a “rebel and heretic” and claimed that the “cataclysm” of Brexit could increase the chance of independence for Wales.

Adam Price said a hard or no-deal Brexit would be a crisis for Wales that could prompt people to turn away from Labour, which has dominated the political scene for a century, and become more open to the idea of independence.

Price has said he will learn lessons from the Scottish National party about putting in place the machinery to win power and said a Plaid government would give the people of Wales the chance to vote for independence by 2030 at the latest.

A week after beating Leanne Wood in a contest for the leadership, Price said these were the “dying days of the British state” but also said he loved England and called for it to free itself from the “shackles” of post-imperialism.

He expressed pride that Plaid had chosen a gay man as leader and said inclusivity would be a key aim. “We’re a small country of 3 million people and we can’t afford to leave anyone behind,” Price said. “We want to be a party for everyone, whatever their gender, race, creed or sexual orientation.”

Price, a miner’s son from Carmarthenshire in south-west Wales, was setting out his vision on Friday at the Plaid conference.

He told the Guardian he had grown up in a Labour family and said if he had been interested in becoming a career politician he would have joined that party rather than Plaid.

“It wasn’t for me,” he said. “I didn’t see it delivering for Wales. To be a member of Plaid Cymru you have to be a rebel, a heretic, a dissident because our message in a nutshell is that it doesn’t have to be this way. We want to turn Wales upside down or maybe the right way up depending on how you look at it. We’re here to create a massive change in the future of our country.”

Price is backing the “people’s vote” on Brexit. “It’s clear to me that a sensible, credible way forward isn’t going to emerge out of the shambolic leadership we have seen since the referendum.

“A cliff-edge, cataclysmic, hard Brexit would be incredibly destructive to the people of Wales. It’s being promoted by people who do not care what happens to our communities.

“We’re left with this situation where we could see the unravelling of the Welsh economy at a 1930s scale. We should take every opportunity there is to stop this madness. The means to do this is take it back to the people.”

Plaid Cymru manifesto promises to protect Wales after Brexit Read more

Price knows he has a big job. Polls still show that most Welsh people do not favour independence and Plaid is the third party in the assembly behind Labour and the Tories.

But Price said if Brexit does happen it could change everything. “In every crisis there is opportunity because crises are wake-up moments. It does feel at times like the last days of the Habsburg empire. The centre cannot hold. There is the opportunity for people to present a different vision. People’s minds are open, possibly in a way that they haven’t been for many, many years. People are listening, looking out for a new direction and it’s our job to present them with that.”

But Price said fine words were not enough: the people of Wales needed to believe Plaid was a credible alternative. He said the example of the SNP was an inspiration.

“It’s often said Labour’s dominance, its hegemony in Wales is impregnable, but that was said in Scotland. They [the SNP] are an inspiration to us but they provide some practical lessons about how to put in place foundations for that sort of electoral breakthrough they were able to achieve.” He said he was talking to SNP colleagues to ensure the best result in the 2021 Welsh assembly elections.

“One of the reasons for the SNP’s success was that they decided to go positive,” Price added. “They set out an inspiring, imaginative vision of a different Scotland. That fired up the imagination. That got people thinking and talking again.”

When he was an MP, Price worked closely with the SNP, notably on his attempted impeachment of Tony Blair, then prime minister, over the Iraq war. He also spent a lot of time in the same lobbies as Jeremy Corbyn, but he is frustrated at the Labour leader’s stance towards the EU. “I’m a passionate European. I’ve got a degree in European community studies. As a Welsh person maybe we see the world differently. A small nation wants to be part of a family of nations.”

Price, who says his mother is English, added: “I love England and I want England to be a decent, prosperous, fair society as well. But England is shackled by the dying embers of this post-imperial state that still harbours ambitions to be what it once was. This is what is driving the resurg ence of a British nationalism and false narrative of some sort of halcyon days of turning the clocks back not just to the 1950s but to the 1850s. England needs to be liberated from that false narrative.”

He did not want independence for its own sake but for a purpose, he said. “Ultimately the only sustainable solution is independence, only through having our hands on the levers of that power will we be able to deliver back the kind of society people want.”