I'm thinking of when he warned Musk in 2012:

"Hassabis told him to add another potential threat to the list: artificial intelligence. Machines could become superintelligent and surpass us mere mortals, -perhaps even decide to dispose of us."

https://time.com/6310076/elon-musk-ai-walter-isaacson-biogra...

You're right that the picture is more complicated than I wrote above. Quickly looking, it seems that Shane Legg was concerned very very early on. I can't find anything tangible about what their strategy was to avoid the danger. It looks like Hassabis had longer timescales than Legg, so perhaps just thought they had more room before it really mattered?