Hi Tim Page,
This is a complex question and not straight forward to answer.
Any non UK income arising while not resident in the UK for a full tax year, is not taxable in the UK.
If you are considered resident for a full tax year, then you can review the guidance on split year treatment, to determine if it can be applied.
In addition, you are taxable on the arising basis on your worldwide income, unless you claim the remittance basis.
The guidance for residence, domicile and remittance would need to be considered and the tests undertaken to determine your residence sand domicile status.
Guidance note for residence, domicile and the remittance basis: RDR1
There is a double taxation agreement between the UK and Ukraine.
Any income arising from a UK employer, while the individual is resident in the UK, is taxable in the UK. Article 22 covers the elimination of double taxation, so that if the income is taxable in the UK, a credit for that tax can be claimed in Ukraine and vice versa.
UK/UKRAINE DOUBLE TAXATION CONVENTION
Paying tax: Homes for Ukraine