SolvedRFIG21530 | Statutory Residence Test (SRT): Temporary non-residence: Treaty non-residence
From HM Revenue & Customs · Residence and FIG Regime Manual
An individual will be Treaty non-resident at any time if, at that time, they fall to be regarded as resident in a country outside the UK for the purposes of double taxation agreements, having effect at that time.
An individual will be Treaty resident in the UK if, at the time, they fall to be regarded as resident in the UK for the purposes of double taxation arrangements having effect at that time.