Slow Horses season 4 will feature infamous Lamb lunch scene as boss teases Joanna Scanlan's mysterious part

Slow Horses has teased more about Joanna Scanlan's part in the upcoming fourth series of the Apple TV Plus hit and we now know the infamous lunch scene her character has with Jackson Lamb will feature.

Scanlan, whose credits include The Thick of It and Wicked Little Letters, joins the show as new Slough House arrival Moira Tregorian where she meets spooks River Cartwright (Jack Lowden), Louisa Guy (Rosalind Eleazar), Roddy Ho (Christopher Chung), Shirley Dander (Aimee-Ffion Edwards), Marcus Longridge (Kadiff Kirwan) and of course, the farting spymaster himself, Jackson Lamb (Gary Oldman).

Speaking to Radio Times magazine, Apple TV Plus boss Jay Hunt says of Scanlan: "I'm not being elusive for any other reason except that there are so many small spoiler alerts, I can tell you very little. But she's extraordinary. And all I would say, and you can see from the photos, is she's sporting a wig and when I first saw it, I thought, 'Wow, OK, amazing'. Joanna's utterly brilliant in it, as you would expect for an actor with such remarkable range."

We also now know for sure (as Radio Times was provided with a picture) that the infamous lunch sequence in "Spook Street", the fourth of Mick Herron's books which is being adapted this time, will feature in the new series.

In the book, River and Louisa head to the pub to discuss the quite extraordinary fact that Jackson Lamb has invited Moira or The Moira as they call her, out to lunch. River says that Lamb might be pulling her leg. "Cruel, even for Lamb," comments Louisa. River replies: "I dunno. Actually, taking her to lunch would be crueler. Besides, taking her to lunch — paying for it? How likely is that?"

We won't spoil the whole scene. But in the book, Moira naively asks Lamb: "Do you treat all your new staff to lunch?" To which Lamb replies: "I treat all my staff the way they deserve".

Apple TV Plus boss Jay Hunt also spoke a little about Hugo Weaving joining the cast. "It's a chilling performance by him, and there are some fabulous scenes with River Cartwright, who learns about his parentage."

The makers tease that the new series opens "with a bombing that detonates personal secrets, rocking the already unstable foundations of Slough House".

Slow Horses season 4 is set to premiere on Wednesday, September 4, on Apple TV Plus.