For example, if a earth connection is required for a temporary test, some of us have been known to connect to the shaft of a heavyweight screwdriver which has been pushed into the soil, right up to its handle.
On most (temporary) occasions when I need an earth connection to ground part of a circuit, I will make use the the gubbins (image attached below) that is plugged into a standard 13A socket. The circular green socket is connected through to the earth pin, by virtue of which the building's electrical installation earth is then extended and made accessible for use.