This dataset contains mobile isotopic (13C/12C) methane measurements and associated data collected around the Fylde, Lancaster, Morecambe Bay, and Barrow-in-Furness in North West England. Data were collected between November 2016 and March 2017. For further details see the following papers: Takriti, M., Ward, S.E., Wynn, P.M., McNamara, N.P., 2023. Isotopic characterisation and mobile detection of methane emissions in a heterogeneous UK landscape. Atmospheric Environment 305, 119774. https://doi.org/10.1016/j.atmosenv.2023.119774 Takriti, M., Wynn, P.M., Elias, D.M.O., Ward, S.E., Oakley, S., McNamara, N.P., 2021. Mobile methane measurements: Effects of instrument specifications on data interpretation, reproducibility, and isotopic precision. Atmospheric Environment 246, 118067. https://doi.org/10.1016/j.atmosenv.2020.118067