The Smith Commission agreement, agreed by all the main parties in Scotland, set out those benefits where power should be devolved to the Scottish Parliament. Tax credits were not amongst those benefits.
However, under the current Scotland Bill clauses, the Scottish Government will have the power to top-up tax credits, as long as it does so through using its own resources. The Smith Commission agreement said that any new benefits or discretionary payments introduced by the Scottish Parliament must provide additional income for a recipient and not result in an automatic offsetting reduction in their entitlement to other benefits. Once the Scottish Government have been clear about how they want to use their new powers, we will work with them to understand the interactions between the reserved and devolved benefit systems.