I think they're describing how you can force the two pins of a europlug into a type-G socket, if you first stick a screwdriver or key or something into the earth pin to open the shutters.
This will give you access to electricity, but the contact area is much smaller than it's designed for (round pins in a rectangular hole), so using it for anything high wattage will end poorly.
An often overlooked part of the BSA spec for type-G sockets is they're supposed to have a flat surface surrounding the socket large enough to prevent you using the earth pin of an upside down plug to do this.
(Not recommended at home kids) use a key (or, safer, an upside down UK Earth pin) in the Earth hole to open the Live/Neutral shutter - then insert the EU prongs. The width of the EU prongs is handily the same as the UK holes.
Touring musicians do it if venues don’t have convertors.
Doesn’t work if the EU plug needs a live earth of course.
This will give you access to electricity, but the contact area is much smaller than it's designed for (round pins in a rectangular hole), so using it for anything high wattage will end poorly.
An often overlooked part of the BSA spec for type-G sockets is they're supposed to have a flat surface surrounding the socket large enough to prevent you using the earth pin of an upside down plug to do this.