The study looked at 50,498 smokers based on data from the Smoking Toolkit Study — monthly surveys of people age 16 and older — dating back to 2006. It estimated in 2017 that between 50,700 to 69,930 smokers stopped smoking, who otherwise would’ve continued without e-cigarettes as a cessation tool.
https://www.cnn.com/2019/10/21/health/e-cigarettes-quit-smoking-uk-study/index.html