The Prime Minister was unable to say whether families will be able to celebrate Christmas together this year, as the Government's top medic predicted a "difficult" few months ahead over winter.
At a press conference officially announcing that social gatherings of more than six people will be illegal in England from Monday, Boris Johnson said it "breaks his heart" to have to impose restrictions on families.
When asked at the first Downing Street briefing since July whether Christmas was effectively cancelled, Mr Johnson told reporters it was "too early to say" whether big parties could be held over the festive season.
He added: "The thing we need now is for everybody to work together to enforce the rule of six and get the current spike down."
The new rules are an attempt to reduce social contact amid a rise in Covid-19 cases across the UK, with a particular peak in infections among young people.
Mr Johnson said the Government had been forced to act because "with the best will in the world people have not, I'm afraid, been totally following the guidelines", he said.
The rules were backed by chief medical officer, Professor Chris Whitty, who said the period between now and spring will be "difficult" as people meet more indoors over the colder months.
Prof Whitty told reporters: "Everybody I think in the country will know, and it has been widely reported that the period over autumn and winter, which is the period when all respiratory viruses have an advantage because people crowd together, more things are done indoors amongst other reasons, it is going to be difficult.
"So the period between now and spring is going to be difficult because this is a respiratory virus.
"I think in terms of the existing restrictions, people should see this as the next block of time that may not last for many months, but it is very unlikely to be over in just two or three weeks."
Despite the new restrictions the Prime Minister struck an optimistic tone saying he is "still hopeful" that "we could be able to get some aspects of our lives back to normal by Christmas".
He pointed to the new "moonshot" approach of mass testing, which could enable theatres and sports venues to test audience members on the day and allow in all those testing negative, as well as enable workplaces to operate more normally.
Mr Johnson said: "In future, in the near future, we want to start using testing to identify people who are negative – who don't have coronavirus and who are not infectious – so we can allow them to behave in a more normal way, in the knowledge they cannot infect anyone else with the virus."