AS MPS CHOOSE today between partial or total bans on smoking in public places they must ask themselves whether lying to promote a cause is ever legitimate.

The question is urgent because the claim that secondary smoking kills is alchemy, not science, and honest anti-smoking lobbyists know it. The theory that cigarette smoke kills non-smokers was dreamt up 30 years ago by anti-smoking activists; only after inventing it did they attempt to prove it.

Dozens of peer-reviewed scientific studies have followed. All point to a compelling consensus that there is no causal link between passive smoking and fatal illness. One of the most comprehensive studies was published in the British Medical Journal in 2003. It concluded: “The results do not support a causal relationship between environmental tobacco smoke and tobacco related mortality.”

That was unsurprising. The International Agency for Research on Cancer notes that of 23 scientific studies into the effects of workplace exposure to second-hand smoke only one found a statistically significant risk for lung cancer. One in 23 is what objective science calls an anomaly.

Even the research director of Action on Smoking and Health admits: “A lot of the studies that have been done on passive smoking produce results that are not statistically significant according to conventional analysis.” In plain English that means there is no convincing evidence that secondary smoking kills.

That is why anti-smokers have resorted to asserting that secondary smoke is responsible for problems such as asthma and bronchitis instead of fatal diseases. It is why they claim that “there is no safe level of environmental tobacco smoke” instead of trying to enumerate a death toll from a syndrome that does not exist.

In 2003 the BMJ’s editor confessed that the debate about secondary smoking is “more remarkable for its passion than its precision”. Sir Richard Doll, the scientist who proved the link between smoking and lung cancer, said: “The effect of other people smoking in my presence is so small it does not worry me.” It should not worry MPs either.

Parliament should assert the primacy of facts. Disliking cigarette smoke is reasonable, but pretending that secondary smoking kills means abandoning science for quarter-truths and irrational sanctimony.