If my batteries have a rested voltage of 12.8v & I connect the solar panel on a cloudy day, the regulator then shows 13.2v (not enough to charge or reach float v) & I connect a light load with the regulator still showing more than 12.8v does this mean that I am not discharging the battery but only using the available solar energy?
Not necessarily.
You can not rely on the voltage you see while charging or discharging to be the voltage of the battery.
Many solar controllers will display the charge rate and the load as separate figures. This is a better indication as to whether you are winning or loosing.