There are tax implications that you will need to consider if you previously left the UK to live abroad and are now returning to live and work in the UK or are considering such a move.
In most cases, if you have returned to live in the UK, you will be classed as resident in the UK and you will be required to pay UK tax on your UK income and gains, and any foreign income and gains.
Your exact liability to Income Tax will depend on whether you are resident and / or ordinarily resident and / or domiciled in the UK. For example, you may not be liable to UK tax on foreign income and gains if your domicile remains outside of the UK. The domicile rules are complex.
When you return to the UK, you will need to register for Self-Assessment if required to do so. For example, if you are self-employed or have income / gains from abroad to report to HMRC.
You would not usually be required to register for Self-Assessment if you are returning to the UK to take up a job as an employee and don’t have any other income to report.
If you had moved abroad and returned to the UK after a period of less than 5 years (temporary non-residence), you may have to pay tax on certain income or gains made while you were non-resident. This doesn’t include wages or other employment income. If you were away from the UK for less than a full tax year then you will usually be liable to pay UK tax on any foreign income for the entire time you were away.