Gary Oldman
Winston Churchill
Kristin Scott Thomas
Clemmie
Ben Mendelsohn
King George VI
Lily James
Elizabeth Layton
Ronald Pickup
Neville Chamberlain
Stephen Dillane
Viscount Halifax
Nicholas Jones
Sir John Simon
Samuel West
Sir Anthony Eden
David Schofield
Clement Atlee
Richard Lumsden
General Ismay
Malcolm Storry
General Ironside
Hilton McRae
Arthur Greenwood
Benjamin Whitrow
Sir Samuel Hoare
Joe Armstrong
John Evans
Adrian Rawlins
Air Chief Marshal Dowding
David Bamber
Admiral Ramsay
Paul Leonard
Admiral Dudley Pound
David Strathairn
President Roosevelt (voice)
Eric MacLennan
Tom Leonard
Philip Martin Brown
Sawyers
Demetri Goritsas
Cabinet Secretary Bridges
Jordan Waller
Randolph Churchill
Alex Clatworthy
Diana Churchill
Mary Antony
Mary Churchill
Bethany Muir
Sarah Churchill
Anna Burnett
Pamela Churchill
Jeremy Child
Lord Stanhope
Brian Pettifer
Lord Kingsley Wood
Michael Gould
Lord Londonderry
Paul Ridley
House of Commons Speaker
Robin Pearce
Ernle Hastings
Michael Bott
Equerry
Olivier Broche
Reynaud
Mario Hacquard
Daladier
Pip Torrens
BBC Producer
Edmund Wiseman
Actor
Hannah Steele
Abigail Walker
Nia Gwynne
Alice Simpson
Ade Dee Haastrup
Marcus Peters
James Eeles
Maurice Baker
Flora Nicholson
Jessie Sutton
Bronte Carmichael
Young Girl on Tube
Roisin O'Neill
Agnes Dillon
John Locke
Oliver Wilson
Joanna Neary
Margaret Jerome
Richard Glover
Brigadier Nicholson
Tom Ashley
Ramsay Staffer
Joshua Higgott
Reporter
Imogen King
Teenage Girl at Tube Map
Miles Gallant
Naval Map-Room Officer
Faye Marsay
Sybil
John Atterbury
Sir Alexander Cadogan
James Harkness
AD Nicholl (Secretary #1)
Joshua James
W D Wilkinson (Secretary #2)
Charley Palmer Rothwell
Christopher Wilson (Photographer)
Patsy Ferran
Maid
Sarah Flind
Cook
Steffan Donnelly
Back Bencher
Kieran Buckeridge
Cecil Beaton
Johnny Otto
Member of Parliament (uncredited)