The near future is a world in which scientists and their AI got it wrong.
Rising temperatures have caused fires that burned landmasses, and the ash from these fires block out the sun. The resulting cold is extreme, like a nuclear winter, and was a mass extinction event for human beings the world over. Electricity grids, communications and services all failed. Societies collapsed. Humanity is reduced to small groups of survivors, scraping by however they can.
Resources are scarce, and bands of survivors resort to violence to obtain enough food and fuel to survive.
A man and his family group have survived the cruel winter by hiding in a house in Surrey, but when a roaming gang starts to ravage the area, they are forced to run. As they flee to safety, the cohesion and tolerance that had kept them going for so long starts to fracture...