Filmed near Larne, Northern Ireland.
Colm Meaney is a taller and bigger man than Timothy Spall in real life, Martin McGuinness and Ian Paisley were the opposite.
Jack the Driver (Freddie Highmore) asks Martin McGuinness (Colm Meaney) if he's seen him on television. That is an in-joke about Meaney, who had a long-running role as Miles O'Brien on Star Trek: The Next Generation (1987) and Star Trek: Deep Space Nine (1993).
In this movie, you can see three actors from Game of Thrones (2011), who played the parts of Barristan Selmy - Kings guard for Dany (sat at the table of the Sinn Fein men), Pod Payne - Tyrion and Brienne's squire (guy at the cash register in the gas station), and Ser Meryn Trant who Arya killed in the brothel (Gerry Adams).
Timothy Spall and Sir John Hurt appeared in the Harry Potter film franchise.