Boris Johnson has laid out new rules for England to curb a second wave of coronavirus, including 10pm curfews, returning to working from home where possible, and halving the number of guests allowed at weddings.
The rule change comes after the country's Covid-19 alert level has risen from three to four - the second highest - meaning the "epidemic is in general circulation; transmission is high or rising exponentially".
The Prime Minister made the announcement during questions in the House Of Commons on Tuesday, following a sharp rise in cases in recent weeks, telling MPs the public must "act now to avoid still graver consequences later on".
"I'm sorry to say that as in Spain and France and many other countries, we've reached a perilous turning point," the PM said.
"A month ago around 1,000 people across the UK were testing positive for coronavirus, today the number has almost trebled."
On new working from home advice, the Prime Minister said: "We are once again asking office workers who can work from home to do so. In instances where working from home is not possible, people should continue their businesses as possible in a Covid secure way".
Boris added that businesses not complying with Covid-19 safety guidelines will be fined, and they will now be a legal obligation.
The PM also confirmed a 10pm curfew will be put on the hospitality industry from Thursday, adding that premises must be fully shut by this time to make it "easier for police" to enforce the rules.
"Pubs, bars and restaurants should operate as table service only except for takeaways," he added, explaining: "We must act to stop the virus being transmitted in bars and restaurants."
Further restrictions announced by the PM include slashing the permitted number of guests at wedding ceremonies and receptions to just 15, while funerals can currently continue under the 30 people regulation at present.
Meanwhile, face coverings will be mandatory for all staff and customers in shops and taxis from Monday, as well as for those in hospitality venues, except for when eating or drinking.
Plus, indoor team sport, such as five-a-side football, is being banned again in England from Thursday, and the phased reopening of stadiums for sports clubs has been put on hold.
In order to ensure people take the rules seriously, the PM upped the fine for a first time offence - be that failure to wear a face mask or obey the rule of six - to £200.
The Prime Minister warned restrictions could be in place for as long as six months, but that they would be constantly reviewed.
While he stopped short of a second lockdown for now, the PM added that if the R (reproduction rate) doesn't go back below one, and people's behaviour doesn't change, then he will be forced to add "significant" extra restrictions.
He added: "I fervently want to avoid taking this step as do the devolved administrations. But we will only be able to avoid it if our new measures work and our behaviour changes."
It comes after more than 57,600 Covid-19 deaths have now been recorded in the England, Scotland, Northern Ireland and Wales combined.
Yesterday, Sir Patrick Vallance and Professor Chris Whitty warned we may end up seeing 50,000 new coronavirus cases a day by mid-October, resulting in "200-plus deaths per day," if we don't "act fast".
The devolved administrations in Scotland, Wales and Northern Ireland have the power to take their own decisions on how best to prevent a second wave escalating.
The Scottish First Minister, Nicola Surgeon, is expected to make an announcement in due course.