People in England who refuse orders to self-isolate will face fines of up to £10,000, Boris Johnson has announced.
Under the new measures, anyone who tests positive for Covid-19 and does not self-quarantine is breaking the law and faces strict penalties.
It will also be illegal for anyone to ignore Test and Trace instructions to self-isolate after coming into contact with someone who is infected with the disease.
Those on lower incomes who face a loss of earnings as a result of going into quarantine will be eligible for a one-off support payment of £500 to help them cope financially.
With new cases of the infection doubling every week, Mr Johnson said the measures were necessary to control the spread of the virus and to protect the most vulnerable from becoming infected.
Announcing the new rules on Saturday night, the Prime Minister said: “The best way we can fight this virus is by everyone following the rules and self-isolating if they’re at risk of passing on coronavirus.
“And so nobody underestimates just how important this is, new regulations will mean you are legally obliged to do so if you have the virus or have been asked to do so by NHS Test and Trace.
“People who choose to ignore the rules will face significant fines.
“We need to do all we can to control the spread of this virus, to prevent the most vulnerable people from becoming infected, and to protect the NHS and save lives.”
The new regulations will come into force in England on September 28.
However, ministers are in discussion with the devolved administrations in Scotland, Wales and Northern Ireland about extending them UK-wide.
It follows a warning by Professor Neil Ferguson – whose modelling led to the original nationwide lockdown – that the authorities needed to act “sooner rather than later” if they were to avoid a return to the infection rates of last March.
Fines will initially start at £1,000 rising to £10,000 for repeat offenders and for “the most egregious breaches”.
These will include anyone who prevents others from self-isolating, such an employer who requires a staff member to come into work in violation of an order.
The penalties are in line with those for people who fail to quarantine for 14 days after returning to the UK from a country not on the list of low risk nations.
Officials said NHS Test and Trace would be in regular contact with individuals told to self-isolate and would report any suspicions that people were not complying to the police and local authorities.
Police will also check compliance in Covid-19 hotspots and among groups considered to be “high-risk” as well as following up reports from members of the public of people who have tested positive but are not self-isolating.
Prosecutions could follow in “high-profile and egregious” cases of non-compliance.
As with other coronavirus rules, there will be specific exemptions for those who need to escape from illness or harm during their isolation, and for those who require care.
Officials said just under four million people on benefits in England would be eligible for the support payments if they lose income as a result of being unable to go into work.
The latest announcement comes just days after the “rule of six” – banning social gatherings of more than six people – came into force.
It will be viewed as further evidence of the concern in Whitehall at the rate of spread of the disease.
On Friday, the Government announced tough new restrictions were being imposed in large parts of England’s North West, West Yorkshire and the Midlands.
It means by Tuesday, when the measures come into force, around 13.5 million people in the UK will be living under some form of additional coronavirus controls.
Prof Ferguson said the country was caught in a “perfect storm” following the easing of lockdown restrictions over the summer, and that swift action was needed to stop the virus spreading out of control.
“Right now we are at about the levels of infection we were seeing in this country in late February,” he told BBC Radio 4’s Today programme.
“If we leave it another two to four weeks we will be back at levels we were seeing more like mid-March. That’s clearly going to cause deaths because people will be hospitalised.
“I think some additional measures are likely to be needed sooner rather than later.”