Best answer by Mw2870
That's an interesting question.
**I'm no tax expert**
Could it be argued that the Interest Award is simply a discount off your overall annual bill?
So if your annual bill comes out at £600 a year, but your DD is £60 a month and have earned (very rough) figures £3.60 Interest Reward. You can say that really your energy bill was £596.4 for the year. Your account is £123.60 in credit, which is rightfully yours to withdraw.
I could only see problems occurring if you were withdrawing more money than you had paid in. But in my example you had paid in £720 and withdrawn £123.60