basically the neutral acts as a return path, and because that was broken it returns through the other earthing system (which in older houses is the copper and galvanised pipes). 63 volts is one hell of a kick, there probably would have been a fair bit of current on that (ive had a couple of wallops in my time and its not fun). You're actually lucky that it didnt kill you, very lucky. it doesnt take much at all (not trying to scare ya but i play with it every day and its something i have learnt to respect, the fact it can bite hard if you dont treat it with care). You'll be fine by the sounds of it, will hurt for quie a few days
sounds like the age / condition of the service wire was the cause.......higher levels of salt and pollution quicken deterioration like that
so a note to anyone who gets a shock from a tap in the future, DONT HESITATE TO CALL STRAIGHT AWAY. it could save you