RFIG20710 | Statutory Residence Test (SRT): Days spent in the UK: Meaning of a day spent in the UK
From HM Revenue & Customs · Residence and FIG Regime Manual
An individual is considered to have spent a day in the UK if they are here at the end of the day (midnight). This is subject to:
If an individual considers that they have been in the UK at the end of the day because of exceptional circumstances, and that this will have a bearing on their residence status see RFIG22220 and RFIG22230. These detail those parts of the SRT where exceptional circumstance days may, or may not be taken into account when counting the number of days spent in the UK.