Lord Justice Underhill began the judgment in this case by noting that, “It is very common in the care sector for workers to agree to “sleep in” overnight [in case] assistance is required in the night”.

The Court of Appeal here had to decide whether the time carers spent on the premises when sleeping must be taken into account when calculating an employer's obligations under the National Minimum Wage (NMW) Regulations.

The Court of Appeal held that, based on the facts at hand, such workers should be considered as ‘available for work’ rather than ‘actually working’. It made it clear that the only time that counts for NMW purposes is time when the worker is required to be awake for the purposes of working.

The court did accept that often ‘the distinctions are subtle’ and that the line dividing “actual work” from “availability for work” will often be fact-sensitive. The Court of Appeal held, however, that a difference in outcome was justified and the appeal was allowed.

Although the Court stressed that this particular decision is limited to ‘sleeping in’ workers, its impact could be felt elsewhere. For example, the Court of Appeal in British Nursing Association v Inland Revenue [2002] EWCA Civ 494 previously held that nurses on a 24-hour call system were considered ‘working’ even when sleeping between calls.

But for other areas, the key issue of contention is likely to be when the dividing line shifts and an employee is deemed to be ‘working’ even when asleep. For example, the Court of Appeal here considered that nighwatchmen in construction companies would be ‘comfortably on the “actual work” side of the line’ considering they have regular, if intermittent, patrolling or monitoring duties throughout a nightshift.

It remains to be seen how the ‘available for work’ and ‘actually working’ distinction will be applied by other tribunals dealing with other areas of work.
http://www.bailii.org/ew/cases/EWCA/Civ/2018/1641.html

The Supreme Court has ruled that the proper interpretation of the National Minimum Wage Regulations means that the sleep-in workers are not entitled to national minimum wage for the periods where they are expected to be sleeping. A review is available here:
https://www.legal-island.com/articles/uk/case-law/2021/march/royal-mencap-society-v-tomlinson-blake-shannon-v-rampersad-2021/