Background and Aims: Due to the COVID-19 pandemic, the survey mode of the Smoking and Alcohol Toolkit Study, a long-running repeat cross-sectional survey, had to change from face-to-face to telephone interviews. This study aimed to assess similarities and differences in sociodemographic, smoking, alternative nicotine and alcohol use estimates between the two survey modes, to understand the potential impacts of this change in methodology on prevalence estimates and trends over time. Design: After COVID-19 restrictions were lifted, we conducted parallel telephone and face-to-face household surveys in March 2022 and in January to March 2024, using a hybrid of random and quota sampling. Data from both years were aggregated. Setting and Participants: People aged 16+ years living in private households in Great Britain. Measurements: Sociodemographic characteristics, nicotine and alcohol use related estimates and their 95% CIs - unweighted and weighted - collected via telephone versus face-to-face in a household. Findings: In the unweighted analyses, the telephone sample included slightly younger and less socioeconomically advantaged groups than the face-to-face sample. After the samples were weighted, estimates of sociodemographic characteristics and nicotine and alcohol use were generally consistent across methodologies, including daily cigarette smoking (face-to-face: 11.1% [10.1-12.1] vs. telephone: 10.6% [9.5-11.7]), non-daily cigarette smoking (face-to-face: 2.7% [2.2-3.3] vs. telephone: 3.4% [2.8-4.1]), and e-cigarette use among people who smoke (face-to-face: 27.0% [23.5-30.5] vs. telephone: 29.3% [25.4-33.3]). However, compared with telephone participants, a lower proportion of face-to-face participants reported currently using e-cigarettes (face-to-face: 6.4% [5.6-7.1] vs. telephone: 10.4% [9.3-11.5]), and a higher proportion reported never drinking alcohol (face-to-face: 31.1% [29.7-32.5] vs. telephone: 25.0% [23.5-26.5]) and never having 6 or more standard drinks on one occasion (face-to-face: 46.6% [44.7-48.5] vs. telephone: 40.2% [38.4-42.1]). More participants provided "don't know" or "refused" responses in the telephone compared with the face-to-face interview, including in response to questions about tobacco use, e-cigarette device type, and the number of standard drinks on a typical day. Conclusions: Face-to-face and telephone surveys generally yield similar estimates of nicotine and alcohol use. However, there may be some underreporting of vaping and drinking in a face-to-face survey conducted in the home compared with telephone.

JB has received unrestricted research funding from Pfizer and J&J, who manufacture smoking cessation medications. LS has received honoraria for talks, unrestricted research grants and travel expenses to attend meetings and workshops from manufactures of smoking cessation medications (Pfizer; J&J) and has acted as paid reviewer for grant awarding bodies and as a paid consultant for health care companies. All authors declare no financial links with the tobacco, e-cigarette, or alcohol industry or their representatives.

This work was supported by Cancer Research UK (PRCRPG-Nov21\100002) and the UK Prevention Research Partnership (MR/S037519/1), which is funded by the British Heart Foundation, Cancer Research UK, Chief Scientist Office of the Scottish Government Health and Social Care Directorates, Engineering and Physical Sciences Research Council, Economic and Social Research Council, Health and Social Care Research and Development Division (Welsh Government), Medical Research Council, National Institute for Health Research, Natural Environment Research Council, Public Health Agency (Northern Ireland), The Health Foundation and Wellcome.

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The details of the IRB/oversight body that provided approval or exemption for the research described are given below:

The University College London Ethics Committee granted ethical approval for the Smoking and Alcohol Toolkit Study (ID 0498/001).

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