The child and working tax credits are part of the tax system and tax credit entitlement is therefore generally based on all income of a tax year which is taken into account for income tax purposes. This includes taxable social security benefits such as widowed parent's allowance. Income which is exempt from income tax is disregarded for tax credits. In particular, maintenance received from a former spouse is disregarded to help lone parents in these circumstances to find and keep work and to encourage the payment of maintenance by the former spouse.
However, the widowed parent's allowance, together with some other income, already benefits from a £300 annual disregard which reduces the amount of such income which is taken into account for tax credit purposes.