The UK government on Wednesday sets out tighter rules on social gatherings to curb the spread of the coronavirus, with concern mounting at rising infection rates among the young.
The law in England will change from next week to reduce the number of people who can gather socially from 30 to six, with some exemptions.
A new public information campaign was also launched to emphasise the importance of hand washing, the use of face coverings and maintaining social distancing.
More than 41,500 people confirmed to have coronavirus have died in Britain, the worst toll in Europe.
The death rate has now fallen to its lowest level since mid-March.
But as in other parts of Europe, cases are increasing, with almost 3,000 daily infections reported in recent days, and concern the outbreak is slipping out of control.
Johnson's office said medical and scientific advisers had agreed that "urgent action is needed", while police had also asked for the rules to be simplified.
Current guidelines stipulate that people must not socialise outside in a group of more than six people from different households.
But the law actually puts that limit at 30 in private spaces.
From Monday, this will be reduced to six, except for large families, weddings, funerals, organised team sports, workplaces and educational settings.
Health Secretary Matt Hancock told Sky News television in an interview: "Abiding by these rules is absolutely vital to protect life.
"We've seen the increase in the number of cases, sadly, in the last few days. We've seen that across Europe, there's a second wave that many countries have experienced."
- Targeted action -
The UK government, which controls health policy in England, imposed tougher restrictions on Bolton, near the northwest city of Manchester, after a "very significant rise" in cases.
Bolton was found to have 120 cases per 100,000 people -- the highest in the country.
Hancock told parliament on Tuesday contact tracing data had shown this was "partly due to socialising by people in their 20s and 30s".
A number of pubs were identified as hotspots, and curbs were put on opening hours of hospitality venues, and locals were banned from socialising with people outside their household.
The latest targeted local restrictions follow similar action in Caerphilly, south Wales, and East Dunbartonshire and Renfrewshire, in the west of Scotland.
The developments come as the UK government is trying to get the economy moving again after nearly three months of lockdown imposed in late March.
It has encouraged people to go back to work and use a government-subsidised restaurant scheme to boost revenues for eateries hit hard by the shutdown.
Critics say such measures have only exacerbated infection rates as young people in particular head out to pubs with scant regard for social distancing.
Hancock warned that although younger people were less likely to develop serious forms of Covid-19, they could easily pass it to those more vulnerable, particularly the elderly. AFP