CGT liable on sale of foreign currency in brokerage or bank account?

Reviewing the HMRC forums it appears that selling foreign currency to buy sterling in an individual's brokerage account sometimes gives rise to chargeable gains or allowable losses, depending on the source of those funds. Please could I check on the following situation - if an individual's brokerage account has built up, over time, a foreign currency balance, from a combination of interest, dividend and share sales, would that need a CGT calculation when the foreign currency is sold to buy Sterling? (Please assume that foreign currency conversion has been correctly included in tax calculations at the time of the interest, dividend and share sales.) If so, would a CGT calculation also be required if that foreign currency were instead first transferred to a bank account and then sold to buy Sterling? Noting the normal simplification since 2012 that foreign currency bank accounts do not give rise to chargeable gains or allowable losses, eg CG78321 as at https://www.gov.uk/hmrc-internal-manuals/capital-gains-manual/cg78321

Hi,
The address to write to is:
Pay As You Earn and Self Assessment,
HM Revenue and Customs,
BX9 1AS
Thank you.