I pay my taxes in a Euro country and have EUR as base country and those forex realized PnL in operations that didn´t involve EUR gave me quite some headache.
Below is the reply I got from IB on the topic, which you might find useful, u can probably change EUR for GBP in your case. Note as well IB does show the PnL in its statements, but other brokers I have where no euros are used don´t, which might end up as an issue with local tax authorities.
Frustrating as well that in a year like 2022 while my portfolio is way down I end up with significant realized gains because of forex (will realize some losses to end up with a 0 PnL but it´s still a hassle).
"Kindly note, Tbill and US-T are denominated in USD and your current base currency is EUR.
Kindly note, if you decide to trade securities such as Tbill and US-T denomated in USD, it will create a Forex gain when trading the products and/or holding them until they expire.
As your account is under IB-IE, based on the OECD AEOI requirement if you are trading Tbill and US-T which should be classified as being a security.
Kindly refer to the KB article below for additional information on what may be reported for the 2022 tax year:
https://ibkb-internal.prod.ibkr-int.co m/node/2784
The gain/loss reported on the Common Reporting Standard Report is capital gain/loss. It shows the gain/loss from the sale of the securities, dividends, and other types of income in which FX may not be included if additional information is received on current laws of OECD. The income reported on the FX income worksheet is ordinary income and it shows income/loss from disposition of a foreign currency. Both the amounts on the Common Reporting Standard Report and the FX worksheet should be reported on the tax return. Please note IBKR reported the amount shown on the Common Reporting Standard Report to the OECD / AEOI to Spain whereas the FX Income worksheet is provided as a courtesy to assist clients figure out their ordinary income/loss from foreign currency transactions with their qualified tax advisor. Income on the FX income worksheet may not be reported to the OECD / AEOI.
Please refer to the below link for more information.
https://www.interactivebrokers.com/en/index.php?f=1554&p=fxpl