Rishi

Is inheritance tax payable on debt repayments made to an estate? My mother has loaned a substantial amount of money to relative (over £500k) who is repaying it in installments (they have a contract for this). I am the sole beneficiary of my mother's estate so when she passes away I will own that debt and the repayments will continue being made to me until the capital is paid off. Would I have to pay inheritance tax or income tax on these repayments?