As the name suggests, the Working Tax Credit (‘WTC’) is intended to provide financial assistance to working people on a low income.
This tax credit extends to self employed people (so the relief is available to foster carers) and you do not need to have any children in order to make a claim (although if you have a child – not including a foster child – then your entitlement will be higher to help with childcare costs).
You will qualify for WTC if you work a sufficient number of hours per week:
HMRC would be unlikely to dispute that a foster carer works a sufficient number of hours to qualify for the WTC.