Strictly, an individual is taxed as a UK resident for the whole of a tax year when they are resident in the UK for any part of it. But, if you leave or come to the UK part-way through a tax year, the year may, by concession, be split.
This means that the UK income tax the individual should pay because they are resident here is calculated on the basis of the period they are living here rather than the whole of that tax year. This has the effect of splitting the tax year into resident and not resident periods for the purposes of calculating the tax due.
But, it is very difficult to provide general advice on the application or not of split-year treatment under the Statutory Residence Test, says Dean Power of expat tax advisers The Fry Group.
The splitting of tax year under the new legislation can depend not only on action in the year in question but also on subsequent action. In particular, while overseas work is mentioned, it would be necessary to ascertain whether the average hours worked in the year after departure was more than 35 hours per week, using a specific calculation. Likewise, residence in the subsequent year would also be based upon hours worked in the year.
Specific and professional advice in these circumstances is definitely preferable.