Overseas Workday Relief
While UK residents are normally subject to tax on their foreign income, unremitted amounts (those not brought into the UK), subject to certain circumstances, are excluded from taxation in the tax year they are received. This is 'overseas workday relief'.
The relevant period is for 'foreign earnings' received in the first tax year immediately following 3 consecutive tax years of UK non-residence, or one of the subsequent two tax years. The recipient of the relief cannot be domiciled in the UK throughout the year (domicile is different from residence) and the duties of employment should have been carried out wholly, or partly, outside the UK.
Generally, this is a complex matter that requires the attention of an expert.