Uk non -resident with income source both inside and outside the Uk

Hi, I am a non-resident of the UK and have income from UK clients, along with income generated in the country I reside in. I need to know if I should be declaring my foreign income on my UK self assessment, along with the UK income. Do I add it to the foreign income pages? Tax is paid in Spain (the country I live in) on both my UK income and Spanish income. Also, as I use tax software there is an option for DTA, should I be checking this box so I'm not charge twice on the income?

Hi,
As non resident you only declare UK income:
Tax on your UK income if you live abroad
Thank you.