People in England who refuse an order to self-isolate could be fined up to £10,000, the government has said.
The new legal duty requires people to self-isolate if they test positive for coronavirus, or are traced as a close contact, from 28 September.
New measures also include a one-off £500 support payment for those on lower incomes, and a penalty for employers who punish those told to self-isolate.
It comes as the PM considers tightening restrictions after a surge in cases.
A further 4,422 new Covid-19 cases and 27 deaths were reported on Saturday.
There were 350 new cases reported in Scotland, the highest daily increase since May, 212 new cases in Wales, and 222 in Northern Ireland.