The actor famous for playing Gerri Kellman on starring opposite Mark Rylance on the London stage, her recent emergency operation, and her thoughts on the US election

When J Smith-Cameron tells me that she wishes we’d been able to meet in a bar rather than a rehearsal room near Waterloo station – we’re on a sofa beside a galley kitchen, listening to the sighs of a cranky immersion heater – I’m caught between believing her, and assuming she’s just playing the trouper. If it takes one to know one, she does indeed strike me as a martini kind of a woman; like Gerri Kellman, the character she played with such brilliance in the TV show Succession, I can just picture her biting decisively on an olive in the low-lit gloom of a Manhattan hotel. But this Thursday evening, she also looks tired, a bit fuzzy at her edges. It’s 6.15pm, and she has been rehearsing Seán O’Casey’s voluble play, Juno and the Paycock, all day. In her shoes – she’s wearing trainers, with a black jumpsuit – I’d already be on my way to a hot bath, an episode of something schlocky and an early night.

It turns out, though, that the purplish shadows below her eyes have relatively little to do with the demands of her director, Matthew Warchus, or her co-star, Mark Rylance. Having arrived in London from New York three weeks ago, disaster struck almost immediately. “I don’t know whether you’re aware of this, but I had to have an emergency appendectomy,” she announces, curling a lock of hair carefully around an ear (a gesture that is very Gerri). “And I’m still sort of getting my strength back.” How horrible, and when she’s so far from home. “Yes, it was a big thing, and my husband [the playwright and Oscar-winning screenwriter, Kenneth Lonergan] couldn’t come because he’s opening a play in New York. But I just feel very lucky. I want to do a whole series about St Mary’s [hospital, Paddington]. They were wonderful. They were rock stars. I sent over a gift for them today because – oh my God – they were so skilful and hardworking, and their work ethic was so aggressive, you know?”