Scotland Bill

I am lost. I fear that I do not understand this no-detriment principle. I may be showing my ignorance coming late to this subject. I thought that I understood the rationale for the Scottish rate: the UK system would remain the same but there would be this variable—take 10 per cent off and top it up. I assume that the allowances, thresholds and system would be the same over the UK. If, for example, a Government believed that more growth could be obtained by going for a lower rate of tax, or higher allowances, and thus lower revenue, that would be the case across the United Kingdom, including in Scotland. The only thing that would move would be the variable rate if the Scots chose to move it. What is this detriment? Are we saying that the Scots could enjoy the advantages of the greater growth in the United Kingdom but that the detriment to their revenue would be compensated through a block grant system? That would be winning twice. That cannot be what is intended. Will the Minister explain how the no-detriment principle works?