I think Paul Clough was charging his entire car, not the battery, so the battery charge light was on all the time.
Your best starting point is to check the voltage of your battery when the car is running. If it is close to 14 volts then your charge light is playing up. If it is lower than 13.5 volts your alternator is playing up. If it is higher than 14.5 volts your regulator is playing up.
Have just woken up, can someone else refine those numbers please, I know I'm close.