Sub Account Feature Tax Question

Hello,

I am the master account holder and based in the UK. However I am managing a partner's account as a sub-account and the partner is based outside the UK.

Sub account doesn't require sub-account holder to verify identity or address. I wonder when it comes reporting tax, I don't need to include sub-account's proceeds in my tax return since it's not my money right?

(I know partner will have to do their tax return in their home country)

I just don't want to get approached later by HMRC and asked why I am not reporting that as part of my tax return since it's not my money and not my account.

Does anyone have experience with this?