"Vaping revolution": 4.3m Brits now use e-cigarettes
One in five ex-smokers said vaping had helped them kick the habit - apparently backing up growing evidence that e-cigarettes can be effective at helping people quit.
A record 4.3 million people are actively vaping in Britain after a fivefold increase in a decade, Sky News reports.
Some 8.3% of adults in England, Wales and Scotland are now believed to be regular vapers - up from 1.7% (about 800,000 people) 10 years ago.
Action on Smoking and Health (ASH), which compiled the report, said a "revolution" had occurred.
E-cigarettes allow people to inhale nicotine rather than smoke.
The NHS says they carry "a small fraction of the risk of cigarettes" because they don't produce tar or carbon monoxide.
The liquid and vapour contain some potentially harmful chemicals but at much lower levels. However, the potential long-term effects of vaping are not yet known.
The ASH report says about 2.4 million British vapers are former smokers, 1.5 million still smoke, and 350,000 have never had a cigarette.
It also found that smokers who vape daily have fewer cigarettes.
However, 28% of smokers said they had never tried an e-cigarette - with one in ten of this group worried they aren't safe enough.
One in five ex-smokers said vaping had helped them kick the habit. This appears to correspond with growing evidence that e-cigarettes can be effective at helping people quit.
Most vapers reported using a refillable tank system, but there appears to be a rise in disposable e-cigarettes - growing from 2.3% last year to 15% today.
Young people appear to be driving this increase, with nearly half of 18 to 24-year-olds saying they used them.
Fruit flavours followed by menthol were the most popular choices for vaping, according to the report - which saw YouGov survey more than 13,000 adults.
ASH said the government now needed an improved strategy to drive down cigarette use.
"There are now five times as many vapers as there were in 2012, with millions having used them as part of a quit attempt," said Hazel Cheeseman, deputy chief of ASH.
"However, they haven't worked for everyone. Just under half of the smokers who have tried them have stopped using them and 28% have never tried one at all.
"Government has said that a 'vaping revolution' will help them meet their ambition for a smoke-free country by 2030 but it won't be enough - we need a comprehensive plan that will help all smokers."