The stopcock in most houses is the main isolator for the water supply into your property and are normally found under sinks or stairs. If a leak occurs on this valve it should be dealt with straight away. When a stopcock has not been operated for sometime it can leak. This means that water is getting past the gland nut. The first thing to do is to try and retighten the gland nut by a clockwise action. As the nut is tightened puts pressure on the packing inside causing it to seal, but this makes the valve stiff to operate. The best action really is to repack the gland. The material for this is readily available at all plumbing merchants or suppliers. Of course only carry this out if you feel confident to do so. If not always call in a professional to do the work. Edgeware Plumbers repair leak on every type of valve.Repacking a gland:1). Close the stopcock to be repacked.2). Undo the gland nut by turning anti-clockwise until it comes away from its housing so it can be slipped further along the spindle. There may be a little water but this is just residual that is draining away.3). Having removed the gland nut, wrap some PTFE tape around the spindle and push it into the void that the packing gland nut screws. Use a small screwdriver to poke it down.4). Replace the nut and tighten enough to squeeze the new material in the gland .5). Open the valve and tighten the gland nut until any water that is still coming through ceases.As stated earlier if you are not a confident DIY person you should call an expert like an Edgeware Plumber for peace of mind and a work guarantee.