“That was my shoes, not my bottom,” says Tamsin Greig, after emitting a squeaky-squelch in a back room at the Royal Opera House. “I mean, I would tell you if it was my bottom.”

In person, the Friday Night Dinner star has such a concentrated stillness and seriousness about her that she catches me deliciously off guard every time she says something funny. Which she does often in the hour we spend together discussing her new (speaking not singing) role in the Royal Opera’s new production of Donizetti’s 1840 comic opera, La Fille du régiment. It’s a kind of magic trick, the way she fixes you with her small, dark, compassionate eyes, nods in slow motion, seeks out the deeper meaning of my questions… then a joke or rare F-bomb will pop out of her like a rabbit from a hat.

It’s a sweetly subversive, self-generated version of what she has done so brilliantly in her most famous sitcom roles – often playing the more “normal”, relatable and empathic character in a cast of eccentrics, trying to hold herself together as situations become increasingly chaotic around her. In Bafta-winning Black Books she is the city shop owner turned temp battling to control her neuroses and bring calm to the more unhinged characters.