My client is a single parent, incapable of work and receives IB topped up by IS which, having been in payment continuously since April 2003, includes a personal allowance for her child and a family premium. Ergo no Child Tax Credit. She is thinking of asking her boyfriend to move in with her. His income is low enough for my client to continue to be entitled to IS if her applicable amount continues to include the personal allowance for her child and the family premium (but not otherwise). Would my client claiming for a partner trigger her migration to Child Tax Credit? If so she would be worse off because her and her partner's combined taxable incomes in the two relevant years exceeds the amount at which maximum Child Tax Credit would be payable.

Thank you.