“They were very, very emotional,” said Ms. Yates. “It was a very powerful experience: people coming together who didn’t know each other, there were tears — and these were all with people who voted the same way.”

For the remainers it was rather like a bereavement group. “There was this huge sense of loss. People talked about waking up on the day of the vote crying and in shock and they didn’t fully understand it themselves. They understood that they were upset but why did they feel so strongly? So it was a bit like a therapy group.”

For leavers there was more a sense of grievance than grief, Ms. Yates said, and a feeling “that they had been left behind, they had been forgotten, it was really this town-city divide.”

Winning the referendum was an unexpected victory — some described it as a gift — but a precarious one.

“They couldn’t quite believe their luck and also said — even back then in 2016 — ‘It will be taken away,’ ” Ms. Yates said. “They were saying, ‘They won’t let us have it.’ There was a real feeling of ‘them and us’ and a feeling of powerlessness. They had managed to get this, but how long they could hang on to it, they didn’t know,” she added.

More recently, Ms. Yates managed to cajole two groups into the same room. “People talked about it being like a civil war,” she said. Indeed, some mentioned Britain’s Civil War, which took place in the 17th century, or even episodes further back in history.