The chief medical officers of England, Wales, Scotland and Northern Ireland made the call in a joint statement.
They said: "The Joint Biosecurity Centre has recommended that the Covid-19 alert level should move from Level 3 (a Covid-19 epidemic is in general circulation) to Level 4 (a Covid-19 epidemic is in general circulation; transmission is high or rising exponentially).
"The CMOs for England, Scotland, Wales and Northern Ireland have reviewed the evidence and recommend all four nations of the UK should move to Level 4.
"After a period of lower Covid cases and deaths, the number of cases are now rising rapidly and probably exponentially in significant parts of all four nations.
"If we are to avoid significant excess deaths and exceptional pressure in the NHS and other health services over the autumn and winter everyone has to follow the social distancing guidance, wear face coverings correctly and wash their hands regularly.
"We know this will be concerning news for many people; please follow the rules, look after each other and together we will get through this."
It comes after the UK Government’s scientific adviser warned there could be 50,000 new coronavirus cases a day by mid-October without any further action.
On Monday, First Minister Nicola Sturgeon said additional lockdown restrictions will “almost certainly” be put in place in Scotland in the next few days.
A total of 255 new coronavirus cases were recorded in Scotland in the past 24 hours, representing 6.3 percent of all those people newly tested.