The last time I visited family in north Wales, I was heartened to see the words “Cofiwch Dryweryn” (“Remember Tryweryn”) emblazoned on several walls. I had read about how the patriotic slogan was popping up, meme-like, all over the country, but I hadn’t seen it with my own eyes. Call me a misty-eyed Welsh nationalist if you like, but I felt quite emotional. Ever since I was a little girl and my father pulled over the car to show me where a village once stood, I had known the story of Capel Celyn, the community flooded in 1965 to create a reservoir for Liverpool in the Tryweryn valley, and how it became a nationalist cause.

The repeated vandalisation of the original graffiti, which the poet Meic Stephens painted in the 1960s and which has now gained charity protection, has led to a kind of viral graffiti campaign, with Cofiwch Dryweryn appearing on walls and slag heaps, alongside roads and near beaches, and even on the side of mountains. It feels like the most significant display of Welsh pride that I have seen in my lifetime.

Since Brexit, there has been a resurgence of interest in Welsh independence. A recent YouGov poll found a third of people in Wales would support Welsh independence if it meant the country would stay in the EU, rising to 42% among 18-24s. This follows independence rallies in Cardiff, Merthyr Tydfil and Caernarfon – where 10,000 people marched. The Brexit party may have come out on top in the European elections, but Plaid Cymru, which has positioned itself as the party for Welsh remainers, took second place with 22.4%, overtaking Labour for the first time in Wales. This “Brexit effect” can partially be put down to the sheer despair many feel about the political chaos in Westminster following the referendum.

In the aftermath of the referendum, in which Wales voted to leave by a majority of 52.5% to 47.5%, I was frequently irritated by the coverage. Wales voted for Brexit, we were told, while commentators were bewildered by the communities who voted to leave despite having benefited from EU funding.

It is a valid point, but it usually ignores the fact that most of the predominantly Welsh-speaking areas voted to remain. It doesn’t surprise me that those who believe their language and culture have been historically oppressed by English politicians would feel they have more in common with, and are more protected by, the EU27 countries (bear in mind that this was before the Catalan crisis). And the potential impact of inward-migration of people from England into Welsh communities on voter demographics had scarcely been covered until research by the geographer Danny Dorling, unveiled last week, suggested what many of us had long suspected: that older English settlers may have swayed the vote in favour of Brexit.

Modern Welsh nationalism is no longer only a question of language, though for those of us who speak Welsh it will always be a part of the conversation. Plaid Cymru’s shift towards a more civic, inclusive form of nationalism, which like the SNP envisages Wales as an independent nation within a larger federal EU, can claim to represent anyone living in Wales – not just those who speak Welsh. At the Merthyr rally, there was more proof that the independence movement has gone mainstream: there were speeches from the former Wales goalkeeper Neville Southall and the former rugby player Eddie Butler. Laura McAllister, professor of public policy at Cardiff University, points out that the conversation has now moved beyond Plaid to other political parties – and to Labour in particular.

‘When the British state is floundering, seeking self-determination – within a larger, protective European framework – has powerful appeal.’ Children hold a pro-EU sign at a rally in Cardiff. Photograph: Matthew Horwood/Getty Images

A year ago, a fifth of Welsh Labour voters supported an independent Wales; now 40% do. For many on the left, myself included, reconciling leftwing politics with nationalism has been a challenge. But Ben Gwalchmai, of the group Labour for IndyWales, says it’s about liberating citizens from the self-serving clique of Westminster. “The IndyWales movement isn’t about pride – it’s about equality, fairness and a better future for all the people of Wales,” he says. “Socialists like us are waking up to its potential to redress a Britain where three countries can vote 65% one way for something in a UK-wide referendum, but it will be ignored if England votes just 3% the other way.”

With its stronger linguistic dimension, Welsh nationalism will always be different to Scottish nationalism. As the Scottish academic Tom Nairn wrote, the latter was more of a “politically oriented separatism … concerned with problems of state and power, and frequently indifferent to the themes of race and cultural ancestry”. But it seems the IndyWales movement is keenly watching Scotland, and a shift towards political nationalism may emerge (it is also worth noting that the pressure group Yes Cymru is deliberately non-party political to broaden appeal). When the British state is floundering, the idea of self-determination – within a larger, protective European framework – has powerful appeal.

Like their Scottish counterparts, Welsh independence campaigners are now rejecting traditional nationalism. That’s not to say the language is no longer important – to speakers such as me, it is part of who we are – but that campaigners have perhaps realised that the mythology of “the overpowering past that nationalism drools over”, to quote Nairn, is less persuasive to voters than the prospect of a fairer society with more devolved powers.

• Rhiannon Lucy Cosslett is a Guardian columnist and author