Where specifically do I declare interest paid on cash balance from a UK investment platform?

In the 2023/24 tax year a UK investment platform I use paid interest on the un-allocated cash balance I maintain for future purchases. This interest did not come from a holding (e.g. a Fund/Gilt). Where specifically (page/box) do I declare this interest on the Self Assessment form? I could not determine if it should be SA100/box 2 (Untaxed UK Interest) or SA100/box 17 (Other UK Income) or another (unknown) box. Not that it is relevant to how the tax system works but, as it was interest earned on cash, I am hoping it would be within the total that the personal savings allowance applies to.

Hi,

This sounds more like peer to peer lending. You would declare this on the additonal information page:

Additional information (2024)

Declare this in box 3. It still forms part of the personal savings allowance.

Thank you.

Thank you for the answer. I came be sure that it definitely isn't anything related to peer to peer because i) neither of the platforms that paid this interest is involved in peer to peer lending, ii) I am aware of peer to peer lending - and reporting gains from it under Self Assessment - as I have done that (and still do) on completely different platforms. Does you answer still stand, i.e. Additional information page, box 3?

Hi,

As not peer to peer, declare as untaxed interest.

Thank you.