On 12 January 2020, the World Health Organization (WHO) confirmed that a novel coronavirus was the cause of a respiratory illness in a cluster of people in Wuhan City, Hubei, China, which was reported to the WHO on 31 December 2019.

[18] Subsequent epidemiological analysis showed that over 1000 lineages of SARS-CoV-2 entered the UK in early 2020 from international travellers, mostly from outbreaks elsewhere in Europe, leading to numerous clusters that overwhelmed contact tracing efforts.

[6] Limited testing and surveillance meant during the early weeks of the pandemic, case numbers were underestimated, obscuring the extent of the outbreak.

[19][20] A legally-enforced Stay at Home Order, or lockdown, was introduced on 23 March,[21] banning all non-essential travel and contact with other people, and shut schools, businesses, venues and gathering places.

[53] The first COVID-19 vaccine was approved and began being deployed across the UK in early December,[54][55] with a staggered rollout prioritising the most vulnerable and then moving to progressively younger age groups.

[59][60][61][62] A third wave of daily infections began in July 2021 due to the arrival and rapid spread of the highly transmissible SARS-CoV-2 Delta variant.

[66][67] In December, the SARS-CoV-2 Omicron variant was confirmed to have arrived and begun spreading widely in the community, particularly in London,[68][69] driving a further increase in cases[70] that surpassed previous records, although the true number of infections was thought to be higher.

[74] All remaining legally enforced COVID-19 related restrictions concluded in Northern Ireland and England during February 2022,[75][76][77] with that step being taken in Scotland (partially extended into April)[78] and Wales by the end of March.

The UK Health Security Agency publishes a weekly "national influenza and coronavirus (COVID-19) report", which summarises COVID-19 levels and other seasonal respiratory illnesses.

[84] In response to the COVID-19 pandemic in the United Kingdom, the UK Government introduced various public health and economic measures to mitigate its impact.

[86] Prime Minister Boris Johnson announced the first national lockdown on 23 March 2020 and Parliament introduced the Coronavirus Act 2020, which granted the devolved governments emergency powers and empowered the police to enforce public health measures.

Across the country, localised lockdowns, social distancing measures, self-isolation laws for those exposed to the virus and rules on face masks were introduced (though certain exemptions were permitted),[88] as well as efforts to expand COVID-19 testing and tracing.

It also forwent the procurement process in contracts in response to shortages of PPE and medical equipment, major issues in the early months of the outbreak, and for developing a contact tracing app.

[92][93] On average, British COVID-19 victims lost around a decade of life; the last time deaths rose so sharply in the UK was during World War II.

[92] Research in 2021 suggests over 1 million people in the UK have had Long COVID, with the majority reporting substantial impacts on day-to-day life.

[98][needs update] The pandemic's major impact on the country's healthcare system, leading to long waiting lists for medical procedures and ambulances, also led to an indirect increase in deaths from other conditions.

[100] In August 2021, a report from Age UK found that 27% of people over 60 could not walk as far and 25% were living in more physical pain earlier this year compared to the start of the pandemic.

[105] The pandemic has had far-reaching consequences in the country that go beyond the spread of the disease itself and efforts to quarantine it, including political, cultural, and social implications.

[111] A 2021 study suggested that the SARS-CoV-2 Alpha variant, which was first detected in Kent, spread internationally via flights originating in London in late 2020.

[119][120] In February 2020, the team at Imperial College, led by epidemiologist Neil Ferguson, estimated about two-thirds of cases in travellers from China were not detected and that some of these may have begun "chains of transmission within the countries they entered".

[124] In a paper on 16 March 2020, the Imperial College team provided detailed forecasts of the potential impacts of the epidemic in the UK and US.

[125] On 16 March, the Prime Minister announced changes to government advice, extending self-isolation to whole households, advising social distancing particularly for vulnerable groups, and indicating that further measures were likely to be required in the future.

This paper and others relied on data from European countries including the UK to estimate that the combined non-pharmaceutical interventions reduced the reproduction number of the virus by 67–87%, enough to stop infections from growing.

[130] In April 2020, biostatistician Professor Sheila Bird said the delay in the reporting of deaths from the virus meant there was a risk of underestimating the steepness of the rising epidemic trend.

[131] In December 2021 scientists from the London School of Hygiene and Tropical Medicine predicted that Omicron could cause from 25,000 to 75,000 deaths in England over the five months to April 2022 unless there were more stringent restrictions, and would probably become the dominant variant by the end of 2021.

[137][medical citation needed] Ali also said "all the commentary to date as to how and why the UK, or Sweden, has done worse than its neighbours is clearly no longer valid".