UK CGT or OIG on sale of mutual funds held in the US

In the case of a US citizen resident and domiciled in the UK who has long-term holdings of (non-reporting) mutual funds in a US-based account that have never generated interest or dividends, but have shown an unrealised paper gain in share price. For the purposes of UK tax, would any disposals of units of these funds be treated as CGT or Offshore Income Gain? And would tax be triggered when the units are sold but the proceeds remain as USD in the US account, or when the proceeds are transferred to the UK? Follow up question: If the sale is treated as OIG, does this count as 'earned income' for the purposes of the annual allowance for tax relief on pension contributions? In other words, while tax may be due at marginal rate if the treatment is OIG, if the proceeds are subsequently paid into a SIPP pension tax relief may be due at a similar rate.

I am also trying to find the answer to the follow-up question, i.e. whether pension tax relief can be applied to OIG.

Hi mordac,
Please have a look here:
Contributions qualifying for tax relief
For guidance on what counts towards employment income for pension matters.
Thank you.