New local lockdowns, further restrictions and tough new fines for failing to self-isolate come into force across parts of the UK on Monday.
People across England will be legally required to self-isolate from this week if they test positive for coronavirus or are contacted by the test and trace service.
If they do not they risk being hit with new fines starting at £1,000 and increasing up to £10,000 for repeat offenders or serious breaches, the Department of Health and Social Care (DHSC) said.
The DHSC also said that police will check compliance in the highest incidence areas and in high-risk groups based on "local intelligence".
High profile and "egregious" cases of non-compliance will be investigated and prosecuted while action will be taken on tip-offs from "third parties" about people who have tested positive but are not self-isolating, the DHSC added.
But people on low incomes who cannot work from home and have lost income as a result will also be eligible for a new £500 test and trace support payment, it added.
Under new rules in England wedding ceremonies will also be restricted to 15 people.
Meanwhile three more council areas in South Wales will go into local lockdown from 6pm on Monday, the Welsh Government has announced.
Neath Port Talbot, Torfaen and the Vale of Glamorgan will be covered by the restrictions, which mean people will not be able to enter or leave the areas without a reasonable excuse.
They will not be able to meet indoors with anyone they do not live with, with extended households suspended.
Restrictions are already in place in Cardiff, Swansea, Llanelli, Blaenau Gwent, Bridgend, Caerphilly, Merthyr Tydfil, Newport, and Rhondda Cynon Taf.
It comes after bans on households mixing came into force in Wigan, Stockport, Blackpool and Leeds on Saturday, while stricter rules are already in force across large swathes of north-west England, West Yorkshire, the North East and the Midlands, as well as parts of west Scotland.
The new restrictions in three areas of Wales means an estimated 17.8 million people across the UK will be living under additional coronavirus measures by Monday evening, on top of those announced by Prime Minister Boris Johnson.
The Government said that, as of 9am on Sunday, there had been a further 5,693 lab-confirmed cases of coronavirus in the UK. A further 17 people had died within 28 days of testing positive for Covid-19 as of Sunday.
Health Secretary Matt Hancock said the Government will "not hesitate" to introduce further measures if case numbers continue to rise.
He added: "Anyone can catch coronavirus and anyone can spread it.
"We all have a crucial part to play in keeping the number of new infections down and protecting our loved ones.
"As cases rise it is imperative we take action, and we are introducing a legal duty to self-isolate when told to do so, with fines for breaches and a new £500 support payment for those on lower incomes who can't work from home while they are self-isolating.
"These simple steps can make a huge difference to reduce the spread of the virus, but we will not hesitate to put in place further measures if cases continue to rise."
Prime Minister Boris Johnson faces a Commons defeat on Wednesday as Tory rebels continue to press the Government to give MPs a chance to vote on coronavirus measures before they come into force.
Conservative former chief whip Mark Harper became the latest backbencher to say he would back the amendment unless ministers back down.
The Government has also pledged an "uninterrupted" supply of personal protective equipment has been promised by the Government for health and social care workers in England as coronavirus cases rise.
The DHSC said four-month stockpiles of items like face masks, visors and gowns will be in place from November.
The DHSC said that six million people had downloaded the NHS Test and Trace App the first day it launched, and this had since risen to 10 million by midday on Sunday.
Ministers are also under growing pressure to review the "hard" 10pm curfew on pubs, bars and restaurants amid criticism that the new rules are leading to revellers filling streets en masse.
Crowds of people were pictured on Saturday night gathering in city centres and piling onto public transport, while long queues formed at off licences after venues kicked customers out at 10pm.
But Culture Secretary Oliver Dowden insisted on Sunday that there was "definitely science" behind the curfew, despite a scientist advising the Government saying he had "never heard" the measure discussed at Sage meetings.
Mr Dowden also said that university students should be able to return home to their families at Christmas if the country "pulls together" and observes the new coronavirus rules.
The Government is under pressure to guarantee young people are not confined to their halls of residence over the festive period because of Covid-19 outbreaks on campuses.
Thousands of students are currently self-isolating in their rooms following a surge in cases at institutions including Glasgow, Manchester Metropolitan and Edinburgh Napier.
Students in Scotland have been told they can return home from university accommodation on a long-term basis, as long as they follow rules on self-isolating.