Hi,
As a non-resident in the United Kingdom, certain countries residency does not guarantee personal allowances shall be given. You need to refer to the country of residence's Double Taxation Agreement with the United Kingdom for further information:
Tax treaties
Further to this, deductions such as underpayments, benefits in kind, would need to be considered also.
In relation to the original response, please follow guidance on tax on foreign income which states you may need to pay UK Income Tax on your foreign income, such as wages if you work abroad, here:
Tax on foreign income
If declaration is required, you would insert this within the SA106 Foreign page.
As per the previous response, you would receive mortgage interest relief at the basic rate.
Thank you.