The leader of Plaid Cymru, Adam Price, has said the general election could signal the start of a movement towards “a new Welsh spirit of independence and optimism”.

Speaking at the nationalist party’s campaign launch, Price put the idea of Wales breaking away from the UK and remaining in the EU as an independent country front and centre of the Plaid campaign.

“That pencil we will all hold in a few weeks could be the start not only of a new politics but a new Wales, a new hope for all of us,” he said.

Plaid’s campaign slogan is “Wales, it’s us”. Price said: “It’s us, the people of Wales, that hold the key to the nation’s future … an independent Wales.

“Now is the time to focus on the future, not the past. I believe like never before the best days for Wales are ahead of us, and 12 December [election day] can be a day on which we declare a new Welsh spirit of independence and optimism and hope by refusing to put our faith in the Westminster parties and instead voting for a future that we ourselves will shape.

“This is the election in which Wales will begin to find its voice as a nation. It will start as a whisper, a still, small voice in the darkness, but it will end with a chorus. Speaking with one voice … Now is our time.”

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Plaid’s launch took place, as it did in 2017, in a hotel close to the Menai strait in north Wales. Two years ago, the then leader, Leanne Wood, focused on the idea of defending Wales from the Tories in London and the Labour-led government in Cardiff, with independence sidelined.

Price took swipes at Boris Johnson and Jeremy Corbyn, complaining Wales was suffering economically and socially because of decisions made in Westminster and Cardiff.

“In calling the third election in just four years, the Westminster parties certainly have given the people the worst Christmas present ever,” he said,

“A political culture that is more toxic than at any time in our history, a poisoned chalice of a choice between two divided parties led by one leader who is resolutely dishonest on Brexit and another who is sadly proven, honestly, clueless. And both of them, as we’ve seen in recent days, advised by public schoolboys who seem to see politics as some kind of pathological game.”

But he emphasised the election should be not about “them” but was instead about “us”. Price argued “almighty lessons” could be learned from the Scottish National party, which had the attention and respect it deserved because of electoral successes.

Price said his party’s priorities included a green jobs revolution, a new approach to care, lifting children out of poverty with universal free childcare and a new £35-a-week payment for every child in low-income families, investing in affordable homes, and tackling crime by creating a Welsh justice system, devolving policing and recruiting 1,600 police officers.

He did not discuss pacts with other pro-remain parties during his speech, but in interviews given beforehand, Price said such agreements were the way to go. He insisted Plaid was the leading remain party in Wales, seeking to stop Brexit through a “final say” referendum, and wanting Wales to become an independent state in the EU.

Introducing Price, the party’s Westminster leader, Liz Saville Roberts, said the times were “dangerous, confused and volatile” but also full of potential. She said the party would look to create harmony with the nearest capital – Dublin – and also with London.

Saville Roberts also attempted to reach out to voters who may not be traditional Plaid supporters. “We are the party for Wales and everyone who lives there,” she said. “If Wales is in your heart, we are the party for you.”

Speaking after the speech, Price said the party was having “positive discussions” about taking part in alliances with the pro-remain parties and hope to make an announcement soon.

He said: “We’ve had extensive discussions, very positive discussions, over many, many weeks and months. In principle, we’re very much supportive of the idea of trying to maximise the number of MPs from pro-Remain parties that are elected from Wales and indeed, of course, there are similar discussions between the Greens and the Liberal Democrats in England.”