about the 4-year FIG regime

I am eligible as a "new 4-year FIG regime" from tax year 2021 per announced in recent budget, please help to clarify below questions: 1. can I claim back the tax on my foreign income which already reported in the tax year 2022-2023? 2. can I choose to be taxed under the new 4-year FIG regime for the current tax year 2023-2024? 3. if I choose to be taxed in the new 4-year FIG regime in future, and I have both UK income and foreign income, is it true that I can keep the Personal Allowance for the UK income while waived the tax of foreign income? Thanks.

Hi YY WONG,
If you have declared overseas income / capital gains in a self assessment tax return and have paid tax on that overseas income / capital gains and there is a tax treaty between the UK and the other country, you can claim a foreign tax credit in your tax return for tax paid overseas.  
The new rules take effect from 6 April 2025, so cannot be applied to any tax year prior to 6 April 2025.  If an individual chooses to be taxed under the new 4-year FIG regime, they will lose entitlement to personal allowances and the capital gains tax annual exempt amount. 
Thank you.