The UK's coronavirus alert level is being upgraded from 3 to 4, meaning transmission is "high or rising exponentially", its chief medical officers have said.
It comes after the government's scientific adviser warned there could be 50,000 new coronavirus cases a day by mid-October without further action.
On Monday, a further 4,368 daily cases were reported in the UK, up from 3,899.
The prime minister will make a statement in the Commons on Tuesday.
BBC political editor Laura Kuenssberg said it sounded "very likely" that pubs and other venues in England will be forced to have 22:00 closing times, alongside other measures.