Damon Yorke is portrayed by a real-life paramedic Greg Lock, who also originated the story and the character. After leaving film school Lock joined the London Ambulance Service and he and the director collaborated on making an "authentic" look at the life of a paramedic, resulting in the final film.
The three jobs the paramedics are seen attending in the shift are delineated by their level of emergency, green (NOT LIFE-THREATENING) amber (SERIOUS, BUT NOT CRITICAL) and red (CRITICAL). Therefore a decision was made by the film-makers to color each scene in their emergency's respective colors. The electrocuted girl is dressed in yellows and has a yellow birthday cake with amber napkins, the old lady has a green shawl over her armchair and green curtains, and the overdose girl has a red scarf and red hair, with Llewelyn wearing a red hoodie.