RFIG21050 | Statutory Residence Test (SRT): Split year treatment: Case 1 - The relevant period
From HM Revenue & Customs · Residence and FIG Regime Manual
A relevant period is any period consisting of 1 or more days that:
begins with a day that falls within the tax year
is a day on which the individual does more than 3 hours work overseas
ends with the last day of the tax year