Is it the end of the world? That was the question on the lips of the Lyons family in Years and Years (BBC One) last night. In the closing minutes of Russell T Davies's dystopian drama, Donald Trump launched a nuclear strike against an artificial island built by China.

Could it happen? Would it happen? And if it did, what on earth would happen next? If there’s anyone who can answer these questions, it’s Dr Jeffrey Lewis, director of the CNS East Asia Nonproliferation Program and a former director of Harvard University’s Managing the Atom Project.

One of the world’s leading experts in nuclear armaments, Lewis is the author of two book-length academic studies of China’s nuclear policy – and a recent novel which imagines a nuclear war between the USA and North Korea sparked by a Trump tweet.

Snappily titled The 2020 Commission Report on the North Korean Nuclear Attacks Against the United States, the novel is written in the style of a government report from the ashes of a post-nuclear-war America. It’s a harrowing read.

“The novel had far more effect than anything else I’d written,” says Lewis, a keen advocate for disarmament. “I have a number of friends in Washington, and everyone’s generally been very positive – even the ones who work for the great orange Cheeto.’”