The P85 form should be completed by you or your tax agent to advise HMRC that have left the UK to live, or are going to work abroad for at least one full tax year.
The completion of the P85 form will ensure that an individual leaving the UK can claim any tax refund they are entitled to and will also help HMRC decide how an individual should be treated for the purposes of UK tax.
The P85 form can be found on the GOV.UK website. There is an online form available as well as a postal form.
An individual’s continuing liability to Income Tax will depend on whether they are resident and / or ordinarily resident and / or domiciled in the UK.
It is also important to consider the National Insurance implications. In some cases, it can be beneficial to continue paying NI whilst abroad specially, to secure state pension credits or if you are considering returning to the UK.