Question

I've had this conversation a couple of time with people, and I've realised that I can't get to a satisfactory answer without some research. And I'm lazy. So I'm going to pose a question... and if I don't get a satisfactory answer here I might well send it to The New Scientist in the hope that they'll answer it.

Assuming that the cost of setting up and maintaining the infrastructure is already taken care of, which is more energy efficient: an electric kettle or a stove top kettle?