A head of production on their first job together, Rhys Ifans and Laura Linney didn’t undergo the standard “chemistry read” to make sure they got on. Which is remarkable, given what their characters would have to do to each other in Onwards and Sideways.

In the Norfolk-set BBC film directed by John Madden (Shakespeare in Love), Ifans would have to nearly throttle Linney while in the grip of night terrors, she’d have to collapse in his arms in a weeping mess having bankrupted herself with a gambling addiction; both situations arising from the neurological condition afflicting their characters: Parkinson’s disease.

But despite being thrown into the deep end in this hugely emotional, often hilarious film, both actors acknowledge an immediate feeling of safety around each other as they embarked on a project that would require them to strip themselves bare. “It’s odd,” says Ifans, “you learn so much about each other so quickly. I couldn’t tell you what kind of car Laura drives. What her home looks like.…