Gary Oldman
Winston Churchill

Stephen Dillane
Viscount Halifax

Lily James
Elizabeth Layton

Ronald Pickup
Neville Chamberlain

Ben Mendelsohn
King George VI

Kristin Scott Thomas
Clemmie

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

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

James Eeles
Maurice Baker

Flora Nicholson
Jessie Sutton

Bronte Carmichael
Young Girl on Tube

Roisin O'Neill
Agnes Dillon

John Locke
Oliver Wilson

Richard Glover
Brigadier Nicholson

Tom Ashley
Ramsay Staffer

Joshua Higgott
Reporter

Imogen King
Teenage Girl at Tube Map

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)