Inside the restricted laboratory compound on the south coast of England, five senior scientists for BAT Industries, the world’s second-biggest cigarette maker, were devising ways to make it harder for people to quit smoking.

At the start of the “brainstorming” session on 11 April 1980, Dr Robin A Crellin, the team research leader, offered an insight. “BAT should learn to look at itself as a drug company,” he said, “rather than a tobacco company.”

Just eight months earlier, BAT scientists had laid out some basic assumptions about cigarettes. A 28 Aug 1979 memo reads: “We are searching explicitly for a socially acceptable addictive product involving: a pattern of repeated consumption; a product which is likely to involve repeated handling; the essential constituent is most likely to be nicotine or a ‘direct’ substitute for it.”

Public disclosure of once-secret industry documents has shown that Big Tobacco privately considered tobacco addictive and harmful at least four decades ago, even as it brushed aside claims that it manipulated nicotine in cigarettes to hook smokers.

Now, a review by the Associated Press (AP) of thousands of BAT documents—some stamped “confidential,” “secret,” and “s-h-r-e-d”—offers new insight into the scale and sophistication of efforts to keep millions of users hooked on nicotine, and the motives driving a project that created a more addictive tobacco.

Taking the reader inside the once-impregnable industry, the papers disclose:

• Why BAT lost its position as the world’s No 1 cigarette maker to Philip Morris and its Marlboro brand in the 1960s (short answer: a nicotine breakthrough)

• Why BAT and its affiliates spent 17 years and tens of millions of dollars to create a new, nicotine-rich, harder-to-kick tobacco (to outdo Marlboro’s nicotine technology and to produce more nicotine at lower cost)

• How vital it was to …