Prime Minister Boris Johnson has urged caution as most legal restrictions on social contact are lifted in England.
There are now no limits on how many people can meet or attend events, nightclubs reopened at midnight, and table service will not be necessary in pubs and restaurants.
Face coverings will be recommended in some spaces, but not required by law.
The PM, chancellor and the health secretary are self-isolating, and there are warnings cases will surge.
Some scientists are predicting that UK infections - currently at about 50,000 a day - could reach 200,000 a day later in the summer.
But with more than 68% of UK adults fully vaccinated modelling suggests hospital admissions, serious illness and deaths from Covid-19 will be at a lower level than in earlier peaks.