Please note - Domicile is not the same as nationality or residence. Usually you have your domicile in the country where you have your ‘real’ or permanent home and you cannot be without a domicile pr have more than 1 domicile at the same time
There are 3 types of Domicile
Domicile of Origin
Domicile of dependance
Domicile of choice
To read more on these click here
If you are domiciled outside the UK and this is relevant to your Income or Capital Gains Tax Liability on the Residency Page on SimpleTax, Click on EDIT
Select the Domicile Tab