Michael Sheen is reportedly so disturbed by the rise of far-right populism he is quitting acting to become an activist, and says he does not know if his relationship with Sarah Silverman will survive.

Sheen will leave Silverman, his partner of two years, and family in Los Angeles and move to Port Talbot in south Wales to combat the wave of “demagogic, fascistic” politics he believes has engulfed the West in the past decade.

He told The Times: “In the same way as the Nazis had to be stopped in Germany in the Thirties, this thing that is on the rise has to be stopped.

“It’s not going to look like this in 10 years’ time. Everything has shifted. The dice are being rolled again.”

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His steel-making hometown, population 37,000, voted for Brexit and the Welsh actor says his frustration at this has formed, in part, the impetus for his decision to begin his activism back where he began. His fears were exacerbated by the ascension of Donald Trump and the tensions stoked by his divisive rhetoric.

Sheen has become increasingly politically and socially active since coordinating the 2011 play The Passion in Port Talbot with hundreds of local people. He works with the children's charity Unicef and has spent months travelling through Britain and Spain looking at community projects he could emulate in his hometown. “The greatest service you can do is to serve the whole, is to serve the story that you’re a part of,” he added. “The story is bigger than any one individual within it.”

In 2015, he gave a blistering, urgent speech about the dismantling of the NHS, the ineffectiveness of modern MPs, who he lambasted for being too “careful, tentative, scared of saying what they feel for fear of alienating a part of the electorate”, and the importance of conviction. Sheen said the overwhelming reaction to his speech, delivered at a rally in south Wales in the pouring rain, made him realise he could rouse support.

He first posited moving back to the UK in an interview with The Telegraph in March. At the time, Sheen presented his plans as “a new chapter” which would also see him move into directing.

Sheen has since clarified his comments in a statement, saying he is only considering putting his acting career on the backburner.

“The interviewer asked me what that meant for my career and I said it might mean I work less as an actor and maybe even stop for a while,” he said on Sunday.

Sheen said he might stop acting “at some point” but added: “I don’t really know yet.”

“I certainly did NOT equate people who voted for Brexit or Trump with a fascistic 'hard right’ that must be stopped," he continued. "The majority of people in the UK, including my hometown of Port Talbot, voted for Brexit. That is the will of the people and is to be respected. That is democracy. Given the concerns around the economy in the area I come from and its industrial history I totally empathise with the dissatisfaction with the status quo that the vote was partially an expression of.