The true and honest answer is that I don’t know, but I can speculate. Among the possible differences between the United States and the United Kingdom, the public anti-smoking campaign has been far more aggressive and blatant in the United Kingdom than in the United States. For example, in the United States, each pack of cigarettes carries the Surgeon General’s (relatively tame and clinical) warning (“Smoking causes lung cancer, heart disease, emphysema, and may complicate pregnancy”) in small print, on the side of the package. In the United Kingdom, the warnings are much more blatant and graphic (“Smoking kills,” “Smokers die younger,” “Smoking may reduce the blood flow and causes impotence,” “Smoking can cause slow and painful death”) in extremely large print, in front of the package. Note that death is never mentioned explicitly in the Surgeon General’s warning in the US, but is frequently mentioned in the UK warnings. (When I saw the warning “Smoking kills” for the first time in 2003, on a pack of cigarettes that my LSE colleague was smoking, I thought it was a joke. It looked like a gag item that one might buy at a novelty store in a shopping mall, like Spencer’s or Hot Topic.)
Several recent studies show that more intelligent Americans are more likely to smoke cigarettes, consistent with the prediction of the Hypothesis, whereas more intelligent Brits are less likely to smoke cigarettes, contrary to the prediction of the Hypothesis. Why does intelligence have opposite effects on smoking in the US and in the UK?