High Voltage cables can explode with very large amounts of force, under short circuit conditions.
This can be caused by a sharp stone or rock gradually working it's way into the cable insulation, by things like road vibration from passing vehicles.
It would make you wonder though, why this toilet was situated so close to the Underground cables in the first place?.
This could have been a certain fatality, had there been a person inside there, when the cable faulted.
Let's face it, these days if you're not young, you're old - Red Green