When Richard breaks into the flat he spray paints "Cheyne Stoking" on the wall. In very sick patients, this is the name of the breathing pattern that is a sign of impending death.
The end credits state the message "In memory of Martin Joseph Considine", this is Paddy Considine's father. Just before Martin died, he kept saying he wanted Paddy to work with Shane Meadows again.
Mark and Marie's two little boys Craig and Matt were played by real life brothers Craig and Matt Considine, Paddy Considine's nephews.
Toby Kebbell was cast at short notice after the actor originally cast as Anthony dropped out due to concerns about playing the learning difficulties realistically.