This tax treatment applies to people coming to reside here or emigrating during the tax year.
Dealing first with individuals coming to reside here they will normally be regarded as resident here for tax purposes from the date of arrival and liable to pay income tax on all income arising from that date on. They get the benefit of a full year’s tax credits although they may only be resident here for part of the year. This benefit applies provided the person will be tax resident here in the following tax year.
For individuals emigrating during the year the reverse treatment applies. They will be given the benefit of a full year’s tax credits for the year in which they leave. For individuals taxed under the PAYE system this would generally give rise to a tax refund being due. Their PAYE would have been calculated by dividing their tax credits evenly throughout the tax year. However if they emigrate half way during the year they have a half year’s unused tax credits to claim against their earnings up to the date of leaving. This relief only applies provided the person will be non-resident in the following tax year.
For people working here on a short term basis they will likely be due significant tax refunds when they leave, assuming they qualify for this relief.