Hi reuters1953,
As the tax return cannot be submitted online, you will need to use a paper tax return.
Archived tax returns and supplementary pages can be found at:
Tax return for Self Assessment.
Supplementary pages can be found at:
Self Assessment tax return forms
FTCR is calculated by referring to the amount charged to UK tax on the income.
Where UK tax is more than the foreign tax, the relief can be up to 100% of the foreign tax paid.
Where UK tax is less than the overseas tax, the relief is up to the UK tax paid.
Thank you.