Adrian Lester plays as Earl of Poynton in The Undeclared War.
Adrian Lester is the top #1 member of the cast and appears in 8 episodes.

Sir David Mark Rylance Waters (born 18 January 1960 in Ashford, Kent, England) is an English actor, theatre director, and playwright. He was the first artistic director of Shakespeare's Globe in London, between 1995 and 2005. His film appearances include Prospero's Books (1991), Angels and Insects (1995), Institute Benjamenta (1996), and Intimacy (2001). Rylance won the Academy Award and BAFTA Award for Best Supporting Actor for his portrayal of Rudolf Abel in Bridge of Spies (2015). Rylance played the title role in Steven Spielberg's The BFG (2016), a live-action film adaptation of the children's book by Roald Dahl, and appeared in Christopher Nolan's Dunkirk (2017), based on the British evacuation in World War II. He appeared as James Halliday in Spielberg's 2018 film Ready Player One, based on the novel of the same name.

Mark Rylance plays as John Yeabsley in The Undeclared War.
Mark Rylance is the top #2 member of the cast and appears in 6 episodes.

Simon John Pegg (born 14 February 1970) is an English actor, comedian, screenwriter, and producer. He came to public prominence in the UK as the co-creator of the Channel 4 sitcom Spaced, directed by Edgar Wright. He went on to co-write and star in the Three Flavours Cornetto film trilogy: Shaun of the Dead (2004), Hot Fuzz (2007), and The World's End (2013). He and Nick Frost wrote and starred in the sci-fi film Paul (2011). Pegg is one of the few performers to have achieved what Radio Times calls "the Holy Grail of nerd-dom", playing popular supporting characters in Doctor Who (2005), Star Trek as Montgomery "Scotty" Scott (2009–2016), and Star Wars: The Force Awakens (2015). He currently stars as Benji Dunn in the Mission: Impossible film series (2006–present), and he played the Chamberlain in The Dark Crystal: Age of Resistance (2019).

Simon Pegg plays as Danny Patrick in The Undeclared War.
Simon Pegg is the top #3 member of the cast and appears in 6 episodes.

Maisie Richardson-Sellers plays as Kathy Freeman in The Undeclared War.
Maisie Richardson-Sellers is the top #4 member of the cast and appears in 6 episodes.

Hannah Khalique-Brown plays as Saara Parvan in The Undeclared War.
Hannah Khalique-Brown is the top #5 member of the cast and appears in 6 episodes.