I have a US 401(k) pension fund from when I was employed in the US (at the time I was resident in the US for tax purposes and non-resident in the UK for tax purposes but a UK citizen). There have been no contributions or withdrawals whilst I have been resident in the UK for tax purposes. I know that when I start to take a income from that 401(k) I will have to report it to the HMRC. However I have also been advised that it is wise to report the existence of the fund in the "additional information" on my UK tax form to ensure there is a clear record of the fund long before I take any withdrawals. I understand that this is quite a common situation but I cannot find guidance on the correct way to report this information and the correct form of words to report it on the form under "additional information"?