Andrew Scott is to star opposite Lily James, Dominic West, Emily Beecham and Emily Mortimer in The Pursuit of Love, Mortimer's adaptation of Nancy Mitford's 1945 novel of the same name for the BBC and Amazon Prime.
Written and directed by Mortimer, The Pursuit of Love is billed as "a romantic comedy-drama about love and friendship" and is set between the World Wars.
BBC One says the three-part series "follows the adventures and misadventures of the charismatic and fearless Linda Radlett, played by Lily James (Mamma Mia! Here We Go Again, Baby Driver) and her best friend and cousin Fanny Logan, played by Emily Beecham (Little Joe, Cruella).
"Their friendship is put to the test as Fanny settles for a steady life and Linda decides to follow her heart, to increasingly wild and outrageous places," the broadcaster teases.
Dominic West (The Wire, The Affair) and Dolly Wells (Dracula, Doll & Em) play Linda's parents, Uncle Matthew and Aunt Sadie Radlett. Fleabag and Sherlock star Scott plays Lord Merlin, their "wealthy and eccentric neighbour". Mary Poppins Returns and Doll & Em star Mortimer plays Fanny's mother, a serial monogamist known as 'The Bolter'.
"I've always loved Nancy Mitford so when I was asked to adapt The Pursuit of Love it was impossible to say no," said Mortimer. "It's an outrageously funny and honest story, whose central character - the wild, love-addicted Linda Radlett - still reads as a radical."
Filming has begun under Covid-19 safety protocols around Bristol and Bath in the UK.