Tax on a loan to family

I have not needed to complete a tax return for several years now as according to my accountant I don't need to as there is nothing that changes in respect of a tax return. I automatically get a tax code each year. I am now lending my grandson a sum of money and we have agreed he will repay me with interest roughly matching what I currently get from Building Society. The BS deducts the appropriate rate of tax on the interest but now I presume I will need complete a tax return. Is this correct and when will I need to do it?

Hi Sigurd The first,
Yes, this will need to be declared as it forms part of your personal savings allowance.
Please refer to guidance here:
Peer to peer lending
Thank you.