For the CEO of a half-billion-pound company, Demis Hassabis’s working day begins very moderately. There is no 5am kale smoothie with The Wall Street Journal, no intensive workout followed by breakfast board meeting. Instead, he arrives in his office beside King’s Cross in London at a sensible hour, spends the day in meetings, then gets home in time for a family dinner with his wife and two children at 7.30pm.

There he is able to relax and put the kids to bed before, at 10pm, beginning what he calls his “second day of work”. And that is when things get a little less moderate.

“I stay up until around 4am,” he says. “Sometimes 4.30, depending how it’s going.”

If the first “day” of his