- Benedict Cumberbatch Alan Turing
- Keira Knightley Joan Clarke
- Matthew Goode Hugh Alexander
- Mark Strong Stewart Menzies
- Rory Kinnear Detective Robert Nock
- Charles Dance Comandante Denniston
- Allen Leech John Cairncross
- Matthew Beard Peter Hilton
- Alex Lawther Joven Alan
- Steven Waddington Supt Smith
- Tuppence Middleton Helen