I wrote a letter to npower's CEO, Paul Massara, which you can read below. But first, an observation, backed by numerous studies, written about by mediators, marriage counselors, therapists, and understood by any parent that has ever tried to get a child to do what they're told: when you demand that somebody do something, you rarely get the result you want. Instead, you either get defensiveness, rebellion, spite, or resentment. You may get temporary obedience, but it rarely lasts, and it never results in the change that you really want. In this case, what we want is for npower to want to pay taxes in the UK. Because that is my end goal, I took a slightly different approach in my letter to Mr. Massara.
If you want to express yourself to npower, but don't think making demands will help, feel free to use as much of my text as you like.