Ian McKellen and Michaela Coel met like their characters in The Christophers do: with a knock on the door.

Coel, taking a break from writing her upcoming BBC-HBO series First Day on Earth in Ghana, turned up at McKellen’s house in London to go over the script with him and screenwriter Ed Solomon.

“I walked into your house,” Coel says in an interview with her and McKellen. “I knew who you were. You were like, ‘Hello! What are you? What are you then?’”

“You looked interesting and beautiful,” McKellen says, smiling. “And you are.”

On-screen chemistry can be elusive, especially when two characters are intended to be diametric opposites.

In The Christophers – which was screened at the Hong Kong International Film Festival earlier this month – McKellen stars as the artist Julian Sklar, a David Hockney-like artist who has not painted in years and now spends most of his days grousing in his dishevelled townhouse while filming personalised videos that trade on his celebrity.

Coel, the creative force behind I May Destroy You, plays Lori Butler, an art restorer hired as Julian’s assistant with the tacit task, while she is there, of forging additional paintings of “the Christophers”, Julian’s most famous and highly lucrative series.