-Mac Just to correct this a bit, Richard Doll was not tasked by the government in 1997 to provide a report on passive smoking - He would have been 85 then which is probably one reason! He did however say on Desert Island Discs in 2001 that he wasn’t personally particularly concerned about the health risks of inhaling second hand smoke. He was approaching 89 years old at the time so that may have had something to do with his personal view!
Probably more importantly, he not only was amongst the first way back in the 1950s to evidence the causal link between smoking and cancers - initially thought to be only lung, but later to other organ cancers, but he also evidenced the causal link to COPD and ischemic heart disease and other cardiovascular diseases. He studied this, ironically using a group of 40000 doctors for over 50 years - right up until his own death. He gave evidence that on average smoking shortened life by 10 years, over half of the study group’s deaths were directly related to their smoking habits and that stopping smoking reduced these risks of early death considerably - by half if smokers stopped by 50 and even more for those who stopped earlier.
You are right though that he indicated a lack of concern about the dangers of secondhand smoke but this was never his principle area of study. But as far as I am aware, he never claimed to have any evidence that second hand smoke posed insignificant risks.
Probably most importantly, the ban on smoking on public places was not only designed to protect non smokers in those places. It’s principle purpose was to make it less socially acceptable given what had been discovered over 40 years of study into the health risks of smoking. It was designed primarily to dissuade new smokers from starting and persuade existing smokers to stop. To be brutal about it - the early deaths of smokers was probably not the principle driver, that would have been the increased public health expenditure treating smokers’ illness prior to death.
At the time of the smoking bans introduction there was limited evidence into the harm caused solely by second hand smoke. This evidence is more available now though - BMJ published an article a few years ago claiming 15% reduction in myocardial infarction since the ban on smoking in public places.