Hi Helen Prinsloo,
Income and capital gains is taxable on the 'arising basis' in the UK on your world-wide income, even if you do not remit the income to the UK.
As you are in receipt of foreign income, you meet the criteria for completing self assessment tax returns.
You can either complete a tax return online or download and print
Self Assessment tax return forms
Have a look at the overview of self assessment, from here, you can register for and submit tax returns.
Thank you.