Mr Richard Cavanagh
I have a Bass Guitar amplifier which appears to still have a charge in the plug after it has been removed from the socket, is this normal and if not what can I do to discharge ?

This is not normal, I would find a professional electrician or amplifier expert and get this fixed.

Capacitors hold virtually an unlimited supply of voltage and when someone or something shorts that out, it can be very dangerous or very painful. I assume that there is a problem within the unit already, so you should not plug it back up to a wall socket and have a pro electronics tech at your local music store take a look at it. It may even be worth repairing since capacitors are very inexpensive.