How to record income that is exempt from tax

Some of the income I receive from my self-employment is paid by an international organisation and is exempt from income tax under an international convention. How do I account for this on my tax return? Or do I simply omit this part of my income?

Hi L Elv,
If it has been agreed by HMRC that it is also exempt you do not need to declare this, you will refer to receiving it in the additonal information section and state under which legislation it is tax exempt.
Thank you.