Long period magnetotelluric (LMT) time series for site Whiteadder (WHI). Funded by NERC, grant number: NE/P017231/1 "Space Weather Impact on Ground-based Systems (SWIGS)". These data consist of measurements of the three cartesian components of the Earth’s natural magnetic field and the natural horizontal electric field at the site. The database will include .xyz files with the LMT data and one document with metadata. See Hübert, J., Beggan, C. D., Richardson, G. S., Martyn, T., & Thomson, A. W. P. (2020). Differential magnetometer measurements of geomagnetically induced currents in a complex high voltage network. Space Weather, 18, e2019SW002421. doi: 10.1029/2019SW002421 for further details.