The Scotland Act 2012 introduces the Scottish Rate of Income Tax (SRIT) which, under current constitutional arrangements, will take effect from 1 April 2016. This is part of the existing UK income tax model and is not a devolved tax. Scottish Ministers will be able to vary the rate of the Scottish Rate of Income Tax, however, it will continue to be collected by HMRC. A Memorandum of Understanding has been agreed between the Scottish Government and HMRC to aid this process (attached).
It will be interesting to see how this will work (If independence is rejected).
This might be an interesting case study on the incentive effects of different marginal rates where there are no barriers to mobility apart from the cost of moving.