Travellers arriving into the UK from Belgium, Andorra and the Bahamas must self-isolate for two weeks from today as toughened quarantine rules come into force.
The restrictions - which are in response to an "increased prevalence" of COVID-19 in these three countries - mean that Britons are now advised against all but essential travel to these destinations.
Tougher rules concerning the use of face coverings also come into effect today.
Face coverings are now mandatory in indoor places of worship, museums and galleries, public areas in hotels and hostels, bingo halls, libraries, cinemas, concert halls, crematoriums, aquariums and indoor zoos.
The new measures come as Preston became the latest part of the UK to see lockdown tightened once again, with council leaders warning young people in particular that they must stick to the rules.
Adrian Phillips, chief executive at Preston City Council, said it was "alarming" to see that the under 30s in the city are contracting coronavirus at a "significant rate".
Rising infection rates have been reported in the Lancashire city - with the rolling seven-day rate of new cases rising from 21.7 per 100,000 people in the week to 28 July to 42.6 per 100,000 people in the week to 4 August.
Current restrictions on household gatherings in Greater Manchester, Leicester and parts of West Yorkshire will also continue.
And Bedford and Swindon have been added to the government's "watchlist" of places where cases are rising.
Households mixing in pubs and houses has been blamed for the rise in coronavirus cases in Preston - with almost half of the cases reported among people aged 30 and younger.
Despite this - and in a marked difference to the lockdown in Leicester - shops, bars, restaurants and other local businesses in Preston have not had to close down.
As of today, people in Preston cannot:
Residents can meet in groups of up to six, or more than six if exclusively from two households, in outdoor areas such as parks and beer gardens.
Households can also visit indoor hospitality venues so long as they don't mix with others.
The restrictions on gatherings will be reviewed again next week, with any changes to be announced by 14 August.
Meanwhile, councils have said they want more power to shut down pubs that fail to comply with social distancing guidelines.
It comes after images of crowded venues shared on social media drew criticism.
This weekend's heatwave is also expected to see people cram themselves into bars and beer gardens to make the most of the weather.
While current guidance says licensed premises should take customer details and ensure they have infection control measures in place, it is still voluntary.
Now, the Local Government Association (LGA) is calling for the guidelines to be made mandatory immediately.
It also wants local authorities to be given stronger powers to enforce the do not have any specific powers to shut drinking establishments under the emergency COVID-19 restrictions.
Councils can only shut pubs and bars under the Health and Safety at Work Act when there is a "serious and imminent risk" to public health.
However, the LGA argues that these laws are less specific and make it more difficult to take swift action.
It wants a temporary COVID-19 objective added to the Licensing Act which will allow councils to shut establishments that fail to collect tracing data or enforce social distancing, or even revoke their licenses.
Nesil Caliskan, chair of the LGA's Safer and Stronger Communities Board, said: "It needs to be mandatory for premises to follow this government safety guidance and councils need the right powers to intervene and take action if necessary."
She added: "While councils do not want to have to shut anywhere down, business owners need to know that councils have the power to act if local communities are put at risk."
A number of pubs and restaurants in Manchester had been trying to "squeeze" customers in despite experiencing a recent surge in cases, the city's night-time economy adviser Sacha Lord said.
He said the venues had a "disregard for the safety of both their customers and their staff".
Meanwhile, the landlord of the Crown and Anchor in Stone near Stoke-on-Trent was forced to apologise after a cluster of 22 cases was linked to his pub.