Smoking costs the NHS more than £5 billion a year - up to five times the previously accepted figure, researchers have revealed.
Illness and disability linked to smoking puts a "huge burden" on the health service in the UK, they said.
Previous studies put the cost of smoking to the NHS at between £1.4 billion and £1.7 billion in 1991.
But the new analysis pushes this figure to £5.17 billion in 2005/06 and the researchers believe this is still an underestimate.
The largest proportion of the money spent on illness caused by smoking was on cardiovascular diseases (£250.8 million), the study showed. The researchers, from the Department of Public Health at Oxford University, also calculated that almost one in five deaths in 2005 were due to smoking.
"We estimate that 109,164 deaths (18.6 per cent of all deaths) in the UK in 2005 can be attributed to smoking (27.2 per cent of male deaths and 10.5 per cent of female deaths)," they wrote in the journal, Tobacco Control.
This figure is similar to previous calculations and "suggests that the overall numbers of deaths attributable to smoking have not changed much in the past 10 years."
The authors used a variety of sources to arrive at their £5.17 billion figure, including a review of studies published between 1997 and 2007 which calculated the cost of smoking. Other data included NHS figures on deaths linked to smoking, NHS costs and information from the World Health Organisation's Global Burden of Disease Project, which looks at illness by region and gender. One in four (25 per cent) men and 23 per cent of women are smokers, based on 2005 figures, the paper noted.
But the authors warned that their figures were an underestimate. "First, we have not included indirect costs in our economic analysis; second, we have not included the burden due to passive smoking; and, third, we have not considered all conditions related to smoking," they wrote.
They noted, however, that the proportion of NHS money spent on smoking - around 5 per cent - has remained similar since the early 1990s. The research comes after a report from the London School of Economics put the cost of smoking to UK businesses at more than £2 billion.