If I have been paid in a foreign currency, how do I declare the income?

For an employed barrister: if you have no equivalent UK income statement, then you should use the earnings in the currency translated into sterling at the exchange rate on 31 March 2024. 

For a self-employed barrister: You must use the total fees you received (your Gross Fee Income) from practice at the Bar (without VAT) during the last calendar year, 1 January 2024 to 31 December 2024