Foreign Tax Credit Relief

I have received £1,974 in dividends from a number of overseas companies. I have entered these figures, by company and country, along with the amount of foreign tax paid in my tax return along with the percentage relief (mainly 15%) I am seeking. Yet I go further with the form I am told it is not possible to calculate the amount of relief I am due. It does give me an optional box to specify the amount I am claiming but I do not know how to work this out - is it 15% 0f £1,974? I have entered all the information asked of me. How am I expected to proceed?

Hi,
Foreign Tax Credit Relief (FTCR) for dividends, varies from country to country, as agreed by the tax treaty. You will need to manually work out how much UK tax is being charged on the dividends, the sum of UK and foreign dividends. Fill out your return completely, leaving the FTCR box empty. Go to the calculation and note the tax being charged against all of your dividends, Self Assessment will add UK and foreign dividends together. Then, work out the relief allowed for each country, using the agreed rate. Add all of the relief sums together. You then have the maximum FTCR that can be claimed. Compare this amount to the UK tax charged on dividends. If the UK tax is more than the foreign tax relief, then the FTCR is the maximum sum you worked out. If the UK tax is less, the maximum is the UK tax charged.
Thank you.