Scotland Bill

I am most grateful to my noble friend. May we just take the example that he gave—that was raised by the noble and learned Lord, Lord Wallace—of people leaving Scotland? If we have an SNP Government who decide to put the top rate of tax up to 60% and a lot of the WILLIEs and other people decide, “We are going to move south” and they tell their neighbours, “Actually we are moving south because we want to be closer to our children”, how will the Government know how much of the tax base has been reduced as a result of the Scottish Government putting up tax and how much as a result of domestic or other normal movement? There is no way that you can tell that effect. Why would it be appropriate to compensate in those circumstances?