Unions are very clear that you should be paid for every hour of your sleep-in shift because when you are required to sleep over in a service user’s home, you are still working. The fact that your work includes sleeping, or that you are rarely disturbed, does not stop it being 'work'! And in reality, overnight careworkers are often the only person at work on the shift. Looking after vulnerable children and adults, they have to deal with challenging demands at a moment’s notice. It is not as if they are free to come and go as they please.
Unfortunately the law does not necessarily agree. In a much-criticised ruling in the case of Royal Mencap Society v Tomlinson-Blake  EWCA Civ 1641, the Court of Appeal has said that the “essence” of a careworker’s sleep-in shift is that they are expected to be asleep, only providing help when required, meaning that if this ruling stands, most overnight careworkers on a sleep-in shift will only qualify for the national minimum wage when they are “awake for the purpose of working”.
UNISON, the union that brought the case, says that this ruling challenges common sense, as well as the established legal understanding of what counts as work.
There will be an appeal against this ruling in the Supreme Court in 2020. In the meantime, the best way to resist cuts to overnight shift payments in the light of this ruling is to join a union and organise.