Hi,
Self Assessment does not provide an official exchange rate, so the onus is on you to use a just and reasonable exchange rate. This means that we cannot give a decisive answer for questions 1 and 2.
The deadline for registering for Self Assessment for the 2023 to 2024 tax year is 5 October 2024. Penalties may be imposed after that date.
You will need to review the tax treaty between the UK and the country where the income arises. If the treaty allows the other country to deduct tax, you can claim a foreign tax credit on your UK tax return. If the treaty confirms the other country cannot deduct tax, you will need to request a certificate of residence and send this to the relevant country.
How to apply for a certificate of residence to claim tax relief abroad
Foreign employment income is declared on SA102 supplementary page and if foreign tax is payable, then you declare this on SA106, so that you can claim a foreign tax credit.
If you are resident in the UK and undertaking remote employment outside of the UK, you will be limited to employee expenses premitted in the UK. You can see guidance here:
Claim tax relief for your job expenses
Thank you.