The data set contains the timeseries of long-period magnetotelluric data collected at 44 sites in Great Britain during the SWIMMR-SAGE project 2021-2023. At each site, five channels were recorded with a 1s sampling rate: The magnetic field components (north-south Bx, east-west By, and the vertical component Bz) were measured using a fluxgate magnetometer manufactured from Lemi, Lviv, Ukraine. The horizontal electric field (north-south Ex, east-west Ey) was recorded using non-polarizable electrodes. The installations were performed by BGS staff following the manufacturers guidelines and best practices. For each site, a folder containing the timeseries data and a pdf containing all relevant metadata are provided. Format: YYYY-MM-DD HH:MM:SS BX BY BZ EX EY Magnetic values in units of nT (10^-9 T). Electric field values are in mV/km. A BGS open report has been published on the NERC Open Research Archive (NORA) describing the motivation, site selection and data collection. It is referenced in the metadata and can be found here: https://nora.nerc.ac.uk/id/eprint/537960/
