Previous research in developed countries have shown that disparities in income translate into significant gaps in health and longevity.
But the extra years of life that, on average, come with being in the highest social brackets are more than wiped out by smoking, showed the study, which tracked mortality rates over a 28-year period among 15,000 men and women entering into old age.
Lighting up likewise cancelled out the survival advantage enjoyed the world over by women, who generally live several years longer than men.
The findings also confirmed that it is never too late to quit: ex-smokers had survival rates much closer to those who had never smoked than to those with a confirmed tobacco habit.
For the study, residents aged 45 to 64 from two towns in western Scotland, recruited in the mid-1970s, were divided into four groups depending on their social class and income level.
They were further divided by sex, and into smokers, former smokers, and "never smokers" who had consistently avoided the tobacco habit.
Survival rates after 28 years spelled out the risks of smoking with stark clarity.Among non-smokers who had never smoked, the survival rate was 65 percent for women and 53 percent for men in the top social tier. The rates in the lowest tier were 56 for women and 36 for men.
For women who smoked, the percentage of survivors dropped to 40 for the most affluent smokers, and 35 for those on the bottom rungs of the social ladder -- fully 30 percentage points less than wealthy non-smokers.
For men the gaps were even larger. Smoking cut the survival rate for the well heeled in half to 25 percent, and for the most income-challenged the percentage dropped to 18.
For both sexes, smoking had a far more devastating impact on mortality than being poor.
"This study provides further evidence that cigarettes indiscriminately damage and kill their users, regardless of social position," said the study, led by Laurence Gruer at NHS Health Scotland and published in the British Medical Journal.
"Smoking itself was a source of greater health inequality than other factors associated with social position in that population."
The results also suggest that moving up the socioeconomic ladder will have little effect on the health of those who continue to puff away.
"The combination of the greatly increased mortality of smokers with the now much lower prevalence of smoking among the more affluent is the major contributor to the widening health inequalities observed in the United Kingdom and other industrialised countries," the researchers concluded.