EIM05275 | Employment income: scale rate expenses payments: accommodation and subsistence payments to employees travelling outside the UK: employee staying in vacant residential property
From HM Revenue & Customs · Employment Income Manual
If an employee stays in vacant residential property, or a serviced flat with cooking and/or laundry facilities, all paid for by the employer or a third party, the employer may reimburse:
for the first 7 days of any stay, 80% per day of the appropriate total residual rate
for the eighth and subsequent days, 50% per day of the appropriate total residual rate
See example 7.