Allen, who rose to fame in the late 2000s with hits such as “Smile” and “Not Fair”, is making her theatre debut in “2:22 – A Ghost Story”, a supernatural thriller that opened for previews at the Noel Coward Theatre on Tuesday.

“I know people say, ‘You’ve been on the stage before’, but it is a completely different experience,” said Allen, who has spent five weeks rehearsing for the role. “I definitely feel a huge amount of pressure.”

The 36-year-old was settling into a new life in New York with her family and had no acting ambitions when, out of the blue, she was offered the part.

“I didn’t have an agent. I wasn’t looking for projects. Then I got a phone call from a casting director, asking, ‘Would you be up for doing a play?’ And I thought, ‘Well, no, not really.’

“But then I thought about it and it was such a great opportunity,” said Allen, who married “Stranger Things” actor David Harbour last year and has two children from a previous relationship.

In “2:22 – A Ghost Story” she plays Jenny, a young woman who believes her new home is haunted. Her conviction causes tension in her relationship with her rationalist husband Sam.

Writer Danny Robins, who also makes his West End debut with the play, said the story was inspired by a friend’s “really credible” account of a supernatural encounter.

“You know, there’s a reason we’ve believed in ghosts since prehistoric times,” he said. “Death is this big, scary, horrible thing, this idea that we just all cease to exist. So we need ghosts in our lives.”

“2:22 – A Ghost Story” runs from Aug 12 to Oct 16.