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

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)

Nick Howden-Steenstra

Sentry (uncredited)