Yes, the worker was engaging in 'time work' on the 'sleep in' shifts, held the EAT in Esparon t/a Middle West Residential Care Home v Slavikovska.
The EAT recognised that it is 'very difficult' to distinguish between cases where the worker was 'at work', being paid to be on the employer's premises 'just in case', and where the worker was 'on call' and not deemed to be working the whole time.
An important consideration is why the employer requires the worker's presence. In this case, the worker was paid to fulfil the employer's legal obligations, under the regulations pertaining to care homes, to have staff available on the premises at all times. It was essential for the employer that staff be there even if they did nothing.
In the circumstances, the Claimant was entitled to be paid simply for being on the premises, regardless of whether she was allowed to sleep on shift.