Millions of people in parts of northern England are now facing new restrictions, banning separate households from meeting each other at home after a spike in Covid-19 cases.
The rules impact people in Greater Manchester, east Lancashire and parts of West Yorkshire.
The health secretary told the BBC the increase in transmission was due to people visiting friends and relatives.
Labour criticised the timing of the announcement – late on Thursday night.
Health Secretary Matt Hancock told BBC Breakfast the government had taken “targeted” action based on information gathered from contact tracing, which he said showed that “most of the transmission is happening between households visiting each other, and people visiting relatives and friends”
The new lockdown rules, which came into force at midnight, mean people from different households will not be allowed to meet in homes or private gardens.
They also ban members of two different households from mixing in pubs and restaurants, although individual households will still be able to visit such hospitality venues.
The changes come as Muslim communities prepare to celebrate Eid this weekend, and nearly four weeks after restrictions were eased across England – allowing people to meet indoors for the first time since late March.
The same restrictions will apply in Leicester, where a local lockdown has been in place for the last month.
However, pubs, restaurants and other facilities will be allowed to reopen in the city from Monday, as some of the stricter measures are lifted.
There is an inescapable fact here – the coronavirus has not gone away and it still thrives on close human contact.
The more we come together the easier it will spread.
We have seen this happen as national lockdowns have been lifted from Europe, to the US, to Australia and more.
Better testing means we can now spot where cases are starting to spike.
The warning signs are in the data with cases climbing in areas like Manchester, Trafford, Salford and Tameside.
The hope is the government has acted quickly enough to suppress the virus with “local restrictions” before it becomes a national problem.
It is now the turn of millions of people in northern England to take the hit, but these local lockdown-tightening measures could happen anywhere.
This is the “new normal” as we buy time until a vaccine is developed.
The health secretary said the move was not an attempt to curtail Eid celebrations after Miqdaad Versi, from the Muslim Council of Britain, said the restrictions were likely to have a “large impact” on Muslim families celebrating Eid.
Asked on BBC Radio 4’s Today programme whether the measures were announced late on Thursday night to stop the celebrations from taking place, Mr Hancock said: “No, my heart goes out to the Muslim communities in these areas because I know how important the Eid celebrations are.”
Also on the Today programme, Mayor of Greater Manchester Andy Burnham suggested that the rise in transmission had been caused in part by gatherings “in multi-generational households”.
Asked whether he meant predominantly the Asian population of Greater Manchester, Mr Burnham replied: “Yes, I do mean that.”
Labour leader Sir Keir Starmer, while welcoming the measures, condemned the government’s decision to announce the changes on Twitter just after 21:00 BST on Thursday as “a new low for the government’s communications during this crisis”.