This section is necessary because of the provisions in Part IV of the Act which enable the Scottish Parliament to vary the basic rate of income tax in respect of Scottish taxpayers, and in some circumstances to do so after the start of the tax year.  It ensures that the Parliament’s exercise of its powers can be accommodated without disruption to the reserved social security, child support and pension systems.
The order-making powers are applicable for all reserved matters under Head F of Part II of Schedule 5, although it is expected that their main use will be in relation to social security benefits and child support.
Entitlement to many social security benefits, including the main income-related benefits of Jobseeker’s Allowance, Income Support, Family Credit and Housing/Council Tax Benefit, is assessed on income net of tax and National Insurance contributions.  Where the Scottish Parliament exercises its power to vary the basic rate of income tax, it is necessary to determine whether a benefit claimant should be treated as a Scottish taxpayer in order to pay the right amount of benefit.  The criteria set out in section 75 to decide whether or not a person is a Scottish taxpayer are (like other tax matters) designed to apply over a full year.  But in order to make a clear decision for benefit purposes, it is necessary to know whether a person is a Scottish taxpayer or not at the point of claim.
Section 75 provides, in certain circumstances, for changes in the Scottish rate of tax at short notice and after the start of the tax year.  It would present operational difficulties for the social security system to reflect changes at very short notice, and could mean that large numbers of benefit claims decided before a tax change might need to be re-examined.
The section provides powers to put the benefit position beyond doubt in both these cases, by specifying who is regarded as a Scottish taxpayer for benefit purposes and what the relevant rate of tax should be.
Commentary Part V: Miscellaneous and General General