Tax in the UK is calculated on the arising basis, however, someone who is resident in the UK, but not domiciled, can elect to use the remittance basis.
If you do not remit the income to the UK, it is not taxable in the UK, until you do remit it to the UK.
You will need to work out your residence and domicile status, to determine if this income is taxable in the UK. You can find guidance on 'Residence, Domicile and Remittance' which will take you to the test you need to apply here:
Guidance note for residence, domicile and the remittance basis: RDR1