The UK has a progressive tax system and so the rate of tax payable increases as income increases. All UK residents have a Personal Allowance which means that the first part of their income is free from UK income tax. For the tax year 2020/21 this is £12,500 but you need to be aware of a change in the system.
The Personal Allowance is also available to people who are not resident in the UK provided they are a citizen of a European Economic Area (EEA) country, which includes all British passport-holders. It also applies to anyone who has worked for the UK government at any time during the relevant tax year.
There is however a change in the way that non-residents, expatriates, claim this allowance which has not been widely publicised so if you are UK non-resident for tax purposes and have income arising in the UK, such as rental income, you need to read on.