Of course Harriet Walter would choose this place, I think, swishing through the revolving door of Arlington in Mayfair into an Art Deco hall of mirrors reflecting monochrome stripes and polished tile. The atmosphere is almost cruelly chic. Where else would a woman famous for her portrayal of stony-hearted, acid-tongued ice queens want to meet?

The waiter takes me to a table in a discreet corner. David Bailey’s black-and-white portraits of 1960s icons look on from every wall. The nearest is of a white-stockinged, kohl-eyed Penelope Tree in 1967, photographed lounging next to an open bottle of champagne, cheekbones like razors. It all makes perfect sense.

So when Walter herself appears, the disorientation is profound. She looks soft — almost fluffy — in a powder-pink herringbone tweed suit and pearl earrings. Her smile is eager and warms up the atmosphere by several degrees. And then there’s her voice. At first she speaks so quietly she sounds almost timorous. It is genuinely hard to believe this is the same person whose sardonic drawl ripped shreds out of her spoiled children in Succession or barked orders as Brutus in a production of Julius Caesar set in a women’s prison. How on earth will she pull off playing Margaret Thatcher in her next TV role, I wonder?