Calculation of capital gain on index future

I have read CG56000P - Capital Gains Manual: Shares and Securities: Futures: contents It is not clear what is the disposal proceed and allowable costs when investors are dealing with index futures in foreign currency. For example if I have bought a Nikkei 225 future contract (in a recognized exchange) at price 25000 points and each contract is worth 1000 yen. The exchange rate of the day is 165. Then I sold the contract at price 30000 and the exchange rate of the day is 175. When buying the contract nothing is paid. Gain and loss are marked to market daily in Japanese yen. Which of the gain calculation is correct (or none of them)? Cost = 25000 * 1000 / 165 = £151515 Proceed = 30000 * 1000 / 175 = £171428 Gain = 171428 - 151515 = £19913 Or since there is no actual cost buying a future contract, I only calculate the net gain in Japanese yen then convert to sterling? Cost = 0 Proceed = Get paid 5000 * 1000 = 5,000,000 yen Gain = 5000000 / 175 = £28571 Another question is, since Japanese Yen itself is a chargeable asset, there would be fluctuation on the amount of yen in the account due to margin collateral. Does this constitute to disposal and acquition of a chargeable asset and causes capital gain/loss? Thank you.

Hi,
We cannot answer questions on specific calculations.
Please see the guidance at CG56000P that you mention and in conjuction with:
CG78310
Thank you.