Hi bmc,
For Capital Gains Tax purposes, the calculation of any gain is calculated in pounds sterling only, using the official exchange rate in place at the time of acquisition and the time of disposal.
Incidental costs of acquisition and disposal can be deducted from the disposal value.
CG15250 - Expenditure: incidental costs of acquisition and disposal.
The official exchange rates can be found here:
Exchange rates from HMRC in CSV and XML format
Archived rates here:
Exchange rates
In the event that an individual remits funds from a foreign bank account to the UK, they will need to calculate the amount of income and gains the account has had since: the day they moved to the UK and the day they remitted the funds to the UK.
This will determine the amount of income and gains that HMRC will tax.
Thank you.