"Congratulations on your successful property sale and the substantial interest payments it's generating for you and your partner! In terms of taxes, the interest income generated by your joint NS&I account will need to be reported on your tax return and may be subject to income tax.
To ensure that you're accurately reporting your interest income, you may want to consider using a tool like
https://www.paystubcreator.net/ to generate professional-looking pay stubs that outline your income and taxes paid. This can help you keep track of your income and ensure that you're meeting your tax obligations."