Another thing Alistair Darling said to the Labour Party conference was:

Our priority is always to look forward and to see what more can be done. Here at home, we have lifted 600,000 children out of poverty. 10 million children and six million families gaining from tax credits. But it's not enough. We must do more. We must eradicate child poverty once and for all.

There is no more, absolute moral obligation.

I agree Alistair.

Your officials have costed the elimination of child poverty at £4 billion. I estimate the gain from abolishing the domicile rule at £4.3 billion

What are you going to do with the change? Enjoy it whilst solving two moral obligations, I suggest.