You will need to take the residence test to determine if you are tax resident in the UK.
You’ll be resident in the UK for a tax year and at all times in that tax year if:
-you do not meet any of the automatic overseas tests
-you meet one of the automatic UK tests or the sufficient ties test
RDR3: Statutory Residence Test (SRT) notes
If you are tax resident in the UK and at all times, you will need to submit a Self Assessment Tax return, declaring your UK employment income.
If you are also required to pay tax on this employment income in the other country, you will also need to complete the foreign section and claim a foreign tax credit of up to the tax paid in the other country.
If split year treatment applies, you will need to submit a tax return, showing the income arising while resident in the UK and tax deducted by your employer.
Split year treatment is claimed on SA109 (residence).
If you choose to submit a tax return online and you need to claim non residence or split year treatment, you will need to purchase 3rd party commercial tax return that includes the residence section and submit it using your government gateway user ID and password.
Self Assessment commercial software suppliers
A paper tax return and the supplementary pages, can be downloaded her:
Self Assessment tax return forms