Background/Aims: In March-2024, the UK government announced plans to introduce a new Vaping Products Duty that will tax e-liquids based on their nicotine strength. This study examined trends in the nicotine strength of e-liquids used by adult vapers and differences in those currently used across relevant subgroups. Design: Nationally-representative, cross-sectional household survey, July-2016 to January-2024. Setting: Great Britain. Participants: 7,957 adult vapers. Main outcome measures: Participants were asked whether the e-cigarette they mainly use contains nicotine and the e-liquid strength. We used logistic regression to estimate time trends in different nicotine strengths used (no nicotine/>0-≤6/7-11/12-19/≥20 mg/ml), overall in England and stratified by main device type (disposable/refillable/pod), age (≥18y), and smoking status. We explored current differences in nicotine strength among those surveyed between January-2022 and January-2024 in Great Britain by main device type, age (≥16y), gender, occupational social grade, history of ≥1 mental health conditions, smoking status, and (among past-year smokers) level of cigarette addiction. Results: The proportion of vapers in England using high-strength (≥20mg/ml) e-liquids increased from an average of 3.8% [95%CI 2.9-5.0%] up to June-2021 to 32.5% [27.9-37.4%] in January-2024 (when 93.3% reported using exactly 20mg/ml). This rise was most pronounced among those using disposable e-cigarettes, those aged 18-24y, and all smoking statuses (including never smokers) except long-term (≥1y) ex-smokers. Of those surveyed in 2022-24 in Great Britain, overall, 89.5% [88.1-90.8%] said they usually used e-cigarettes containing nicotine, 8.7% [7.5-10.0%] used nicotine-free e-cigarettes, and 1.8% [1.2-2.4%] were unsure. The proportion using ≥20mg/ml was higher among those mainly using disposable (47.9%) compared with pod (16.3%) or refillable (11.5%) devices; never smokers (36.0%), current smokers (28.8%), or recent (<1y) ex-smokers (27.4%), compared with long-term ex-smokers (13.9%); and younger (16-24y; 44.2%) compared with older (≥25y; range 9.4-25.1%) age groups. There were no notable differences across other subgroups of interest. Conclusions: Use of high-strength nicotine e-liquids in England has increased sharply in recent years. Most adult vapers in Great Britain use e-cigarettes that contain nicotine but different subgroups use different strengths: they tend to be higher among those who mainly use disposable devices, those aged 16-24y, and lower among long-term ex-smokers.