Speaking ahead of the New Year’s Day episode, Cumberbatch said: “The babies have been pretty amazing.

“I’m a father and I know how difficult it is to get anything in tune with a baby’s schedule.

“It keeps you in the moment and it stops you being precious about your work.

“I love those elements that make it more difficult.”

As is conventional in television, the one baby character will be played by several real-life babies, with filming taking place in between naps and feeds under close supervision.