Labour would support the Welsh government getting the power to vary incometax rates after a referendum if the Barnett formula that decides much Welsh spending is reformed and if it can be shown that it would be good for Wales.
"Spending power" takes into account both the core "formula grant" which councils get from central government and other income - council tax and other grants.
For example, we agree with Silk that any future devolution of incometax powers is contingent on a period of assignment, reform of the Barnett formula and a referendum to test the will of the Welsh people.
Formula apportionment would allow tax bureaucrats to concoct a system for arbitrarily changing the existing distribution of business income, with a clear goal of forcing companies to over-state their taxable income in high-tax nations.