The reason for the UK triangle is that the orientation is set, so you know which of the supply wires is live and which is neutral - and if the plug is half remo

The reason for the UK triangle is that the orientation is set, so you know which of the supply wires is live and which is neutral - and if the plug is half removed the top exposed pin is ground so if anything fell down onto the socket it wouldn't touch a hot pin Extreme I know - whoever designed the UK plug was obviously paranoid.