Recently I had to turn off the water at the stopcock which is located in my kitchen. The stopcock itself started to leak. A neighbour came in and explained to me that just below where the tap handle is, there is a nut that sometimes works loose when you turn the tap (stopcock) handle. He tightened that up with a wrench and it seems quite ok now.
However, a plumber that I had contacted said that the stopcock would need 'packing' otherwise it would leak again the next time the stopcock is turned. What is exactly is this 'packing'? And is it necessary or is he after an easy few quid?