Recently, one of my power/extension cables stopped working, and of course I had to find out why…… opening the plug showed that the Neutral wire hold-down screw had loosened and said neutral was no longer making connection. Simple to repair, but what was REALLY shocking (literally) was that the same thing had happened to the Earth (Ground) connection, and that could have had potentially fatal consequences. Please read the following article, it may save your life. Written for the US market, it applies to this side of the pond just as much……
http://www2.fender.com/experience/tech-talk/grounded-electrical-connections/