Map of the National Grid in Great Britain, featuring all transmission lines and substations at 220 kV and above. Derived from OpenStreetMap data in February 2023, which is, as far as I am aware, an accurate representation of the current grid.
Note that the National Grid in Scotland includes lines operating at 132 kV, but they are not included in this diagram for consistency.

Onshore and offshore wind farm connection cables at 220 kV and above are included even if they are not operated by the National Grid.
Own work
Russss, OpenStreetMap contributors