An individual acquires a domicile of origin when he is born. Normally this would be the fathers domicile at the date of birth, however, if your parents were unmarried, it is your mothers domicile that you will take.

Your domicile of origin, would be where you were born. This domicile has a degree of permamence, and the burden of proof would be on the IR to show that you have changed your domicile, by making a domicile of choice. The acquisition of a domicile of choice is regarded as a serious matter.

After the age of 16 you could change your domicile. In order to do this 2 aspects must be fulfilled.

Firstly, you would need to make the UK your sole/primary residence

Secondly,you must intend to remain here generally for the rest of your days, or until something occurs to make yoy change your mind.

The first aspect is easily satisfied, if the UK is now your sole residence. In order to retain your foreign domicile (of origin) you would need to show sufficient intention that the UK would not be your home indefinitely.

On a practical level,  it is important to try & establish your non UK domiciled position with the IR.

One method of testing your domicile position would be to have unremitted foreign income, as such income would not be taxable unless you are UK domiciled. A claim for non domciliary treatment could be made on form DOM 1 or on your tax return. The IR will then respond with a ruling.

There are a number of issues that the IR will look at to determine whether you have established a UK domicile of choice. The best way of substantiating a claim that you do not intend to stay in the UK indefinitely is often to keep a home or other property in your country of origin. You should also ensure that your will is under the law of your country of origin, and that you continue to have social/personal/business connection with that country.