Magnetotelluric data for the Halloween 2003 magnetic storm in the vicinity of Uppsala (UPS), Sweden and Eskdalemuir (ESK), Scotland geomagnetic observatories synthesized from geomagnetic observatory data from INTERMAGNET. The data were generated to facilitate comparison of the ground effects of the Halloween 2003 magnetic storm in Sweden and Scotland. The data demonstrate the greater risk of hazardous storm-time electric fields being generated in southern Sweden compared to central Scotland and are further described in the gold open access paper: F. Simpson and K. Bahr, 2020a. The role of tectonic-plate thickness and mantle conductance in determining regional vulnerability to extreme space weather events: possible enhancement of magnetic source fields by secondary induction in the asthenosphere. Space Weather, accepted, doi pending. The synthesis technique that enables electric fields to be estimated from geomagnetic observatory data is described and validated in the following gold open access papers: F. Simpson and K. Bahr, 2020b. Nowcasting and validating Earth's electric field response to extreme space weather events using magnetotelluric data: application to the September 2017 geomagnetic storm and comparison to observed and modelled fields in Scotland, Space Weather, 18, e2019SW002432, https://doi.org/10.1029/2019SW002432. F. Simpson and K. Bahr, 2020c. Estimating the electric field response to the Halloween 2003 and September 2017 magnetic storms across Scotland using observed geomagnetic fields, magnetotelluric impedances and perturbation tensors, JSWSC, swsc200019, 10, (48), https://doi.org/10.1051/swsc/2020049.