The new measure comes into effect on Tuesday, and applies to all variants of Covid-19, the Department for Health and Social Care (DHSC) said, with those who test positive or develop symptoms forced to self-isolate.
People who have been double-vaccinated are to be told to take daily lateral flow tests for a week after coming into contact with a coronavirus case.
It replaces the requirement for all omicron contacts to self-isolate for 10 days, in what the DHSC labelled an attempt to reduce pressures on people’s everyday lives which will help to identify asymptomatic cases and monitor the virus’s spread.
Government disease experts have warned that, with the seemingly more infectious omicron variant likely to become dominant in the UK by next week, the country could see one million cases by late December.
With cases set to rise steeply, the so-called “pingdemic” which caused businesses across the country to close in the face of soaring case numbers after Boris Johnson declared “Freedom Day” on 19 July may have been fresh in officials’ minds while deciding to ease omicron isolation rules.
People who have not been vaccinated must continue to self-isolate for 10 days if they come into contact with any variant of the virus, the DHSC said.
“The omicron variant is quickly gaining ground in the UK and is expected to become the dominant strain by mid-December,” said Javid Javid, the health secretary.
“We are taking this proportionate and more practical measure to limit the impact on people’s day to day lives while helping to reduce the spread of omicron.
“Vaccines remain our best defence and I urge anyone yet to get a first and second jab to come forward and those eligible for a booster to get boosted as soon as possible.”
People will be contacted by the Test and Trace service or shall receive a notification from the NHS Covid-19 app to tell them they are a contact of someone who tested positive and what action they need to take, the government said.
Contacts will be advised to get a free box of seven lateral flow tests from the NHS, either through pharmacies, schools or home delivery by ordering online. Test results should be reported to Test and Trace via the government website or by calling 119.
The new daily testing rule also applies to all children over the age of five, regardless of their vaccination status.
The announcement came after early research from the UK Health and Security Agency (UKHSA) suggested that two doses of current vaccines may be less effective against omicron than the delta variant – but that booster jabs offer between 70 and 75 per cent protection against symptomatic infection.
Protection against severe disease and death are expected to be much higher, the agency said, adding that its early results should be treated with caution.
Elsewhere, modelling by scientists at the London School of Hygiene and Tropical Medicine who are advising the government indicated the UK could see between 25,000 and 75,000 deaths by April in worst-case scenarios.
Dr Jenny Harries, chief executive of the UKHSA, said: “If you are identified as a contact of someone with Covid-19, taking a rapid daily test – and only needing to isolate if it is positive – will help reduce the spread of the virus and minimise its impact on our everyday lives over the coming weeks and months.
“Rapid tests are freely available in pharmacies and online. Our latest analysis shows that boosters provide the best protection against the omicron variant, please go forward when you are called.
“If you haven’t had any vaccine, a first and second dose still gives you protection against becoming seriously unwell. Don’t worry about stepping forwards now – you will be warmly welcomed by our vaccination staff and I would strongly advise you to get vaccinated as soon as possible.”