Purchase a cistern repair kit (about £1 or so and u will find a new nozzle,a split pin , a new nozzle washer and a new water inlet washer.Turn off the cold water main. Remove the split pin and extract the ball and arm.Remove the complete valve from the water inlet.Unscrew the valve end from the body and replace the washer.Push out the old nozzle and replace.Replace the water inlet washer.Rasssemble and use the new split pin to hold the ball and arm.That should do it.
George Bowden, November 2008