Induction cooktop hardly consumes any electricity. Electric kettle, I believe has a heating element that consumes more power.
The energy required to heat and boil 1 Liter of water or milk will remain the same whether you provide it via burning natural gas or LPG, or via using heating coils, or induction, or even nuclear power.
If what you speak of induction cooktop is true, then the liquid in the pan will never boil!
@Ray, there two unrelated things to consider:
1. The efficiency of heat transfer from the pot/pan/vessel to the liquid/food only change based on the material of the vessel and the shape of the vessel (wide open mouth = more heat lost to the atmosphere, and therefore less available for the food)
2. The efficiency of heat transfer from heat generation mechanism to the vessel. This is where induction scores the best. Since what is transferred from the mechanism to the vessel is NOT heat but electricity. Therefore nothing can be lost to the atmosphere.
In case of heating coil, there is a significant loss of heat from the heating coils to the atmosphere, unless the heating coil is almost touching the vessel and the backside of the coil has a mirror (to reflect all the heat back towards the vessel).
In case of a flame, there is even higher losses to the environment - especially when the flame is large.