Ray Winstone plays an Alzheimer's patient on the run in his new film, Ashes – an unsettling drama inspired by the young director's father. Laura Barton visits the very, very rainy Isle of Man set

Under the glare of huge floodlights, the fir trees appear to be dead. They stand pale and brittle, ghostly spines pressed against the darkness. The night is still; then, through the quiet trees, crashes the stumbling form of Ray Winstone, followed at speed by a wild-eyed Jim Sturgess. Winstone lumbers on. Sturgess bounds after him, bellowing: "Dad! Dad! Dad!!!" And somewhere, in a clearing, stands Lesley Manville, her mascara blurred, rain trickling through her fine blond hair.

This is day nine of the Ashes shoot. It's the early hours of the morning, bitterly cold, and we are in a forest on the Isle of Man. The rain falls furiously, beating a steady tattoo against the crew's cagoules and camera covers,...