taxation question regarding power of attorney over an account

Hi guys, wonder if anyone here has any knowledge of this situation.
I am currently a resident of the UK. Now, if i have the power of attorney over a US-based brokerage account, will the capital gains in that account be taxed due to my UK residency? I should mention that the account holder is neither a Uk nor US resident.

Thanks,
alientrade

Tax is payable by the person or business who is the beneficial owner of the US-based brokerage account. The person who has power of attorney is not taxable.