As coronavirus began to spread rapidly across the globe, governments around the world scrambled to try to slow the rate of infection and contain the virus.

On 23 March 2020, then prime minister Boris Johnson announced a nationwide lockdown in the UK, ordering people to "stay at home".

More than three years later, at the centre of the COVID-19 inquiry are hundreds of documents, WhatsApp messages and thousands of bereaved families waiting for answers.

Government officials have been called out for breaking the rules during lockdowns, something which the inquiry is set to explore.

The UK was also heavily criticised for being too slow to introduce things like lockdowns and social distancing.

What is the COVID inquiry trying to find?

The UK recorded one of the world's highest total number of deaths from COVID, with more than 175,000 reported by the time Boris Johnson stood down.

The inquiry doesn't have the power to bring criminal or civil charges against individuals or bodies, and cannot force the government to take on its recommendations.

It has been set up "to examine the UK's response to and impact of the COVID-19 pandemic and learn lessons for the future".

It will hold public hearings, which are expected to last until 2026.

It has also encouraged people to share their experiences through the Every Story Matters section on its website.

The inquiry is expected to last for years, with no date given for when it will end, and the cost is likely to run into tens if not hundreds of millions of pounds.

The chair of the inquiry is Baroness Hallett.

She has the power to compel the production of documents and call witnesses to give evidence under oath.

You can read more about who Baroness Hallett is here.

What are the 'modules'?

The inquiry is split into several modules - interim reports will be produced at the end of each one.

There are four active modules and several modules that will begin later.

Module one focuses on the UK's preparedness for a pandemic and the inquiry will begin hearing evidence for this module on 13 June. Each hearing will last for six weeks.

Module one looks into whether the pandemic was properly planned for and whether the UK was "adequately" ready for that eventuality.

The inquiry website says the module will also "scrutinise government decision-making relating to planning and seek to identify lessons that can be learnt".

Module two has been split into parts A, B and C.

First, the module will look into the "core political and administrative governance and decision-making for the UK".

Sections 2A, B and C of the inquiry will travel to and be hosted by the devolved nations.

2A will look into Scotland, 2B will look into Wales, and 2C will look into Northern Ireland.

There is also a separate Scottish COVID-19 inquiry taking place and will begin in July.

The module will also look into the decision-making around non-pharmaceutical measures and the factors that contributed to their implementation - things like face coverings, handwashing and meeting outdoors.

Module three will look at the government and public response to COVID-19 as well as analyse the impact the pandemic had on healthcare systems, patients and healthcare workers.

The inquiry says this will include healthcare governance, primary care, NHS backlogs, the effects on healthcare provision by vaccination programmes as well as long COVID diagnosis and support.

Module four will consider and make "recommendations" on different issues relating to the development of COVID-19 vaccines and the implementation of the vaccine rollout programme in England, Wales, Scotland and Northern Ireland.

The inquiry says it will also look into issues relating to the treatment of COVID-19 through both existing and new medications.

It adds: "There will be a focus on lessons learned and preparedness for the next pandemic."

This section will also look at public concerns about vaccine safety and the current system for financial redress under the UK Vaccine Damage Payment Scheme.

Modules that are not yet announced but will be revealed in more detail in the coming months include:

The care sector; government procurement and PPE; testing and tracing; the government's business and financial responses; and health inequalities and the impact of COVID-19.

Others include education, children and young persons, and other public services, including frontline delivery by key workers.

Key controversies in the pandemic

Mr Johnson and his government have been accused of breaching several COVID-19 rules and the former prime minister has now been asked to hand over WhatsApp messages, documents and notebooks as part of the inquiry.

Here are some of the gatherings that took place:

• 15 May 2020: Cheese and wine party at Downing Street

• 20 May 2020: About 100 people were invited by email for drinks in the garden at Number 10

• 18 June 2020: Farewell gathering to mark the departure of a Number 10 private secretary

• 19 June 2020: Boris Johnson's birthday party

• 13 November 2020: A farewell gathering for Dominic Cummings

• 27 November 2020: Leaving drinks for Number 10 aide Cleo Watson

• 10 December 2020: The Department of Education holds a gathering to thank staff

• 14 December 2020: The Conservative Party held a gathering at its headquarters

• 15 December 2020: A photo published in The Sunday Mirror showed Mr Johnson and other colleagues taking part in a Christmas quiz

• 16 December 2020: The Department for Transport apologised after reports of a party in its offices

• 17 December 2020: Leaving drinks were held for the civil service COVID taskforce

• 18 December 2020: Allegra Stratton was caught on video joking about a Number 10 party. She said: "This fictional party was a business meeting, and it was not socially distanced" - she later resigned

• 14 January 2021: Farewell drinks for two private secretaries - police determined this event did breach rules at the time

• 16 April 2021: Two parties were held before Prince Philip's funeral

Read more from Sky News:
How Boris Johnson defends each of his partygate statements to parliament
All the pictures published in the Sue Gray report

The WhatsApp messages and legal battle

For the investigation, the inquiry needs as much information as possible to understand what happened during the pandemic and how the government conducted itself.

Chair of the inquiry, Baroness Hallett, had ordered the government to hand over documents - these included messages between Mr Johnson and his fellow ministers.

But Rishi Sunak's government has pushed back.

On 1 June, the inquiry confirmed that it had received a response from the Cabinet Office seeking to commence judicial review proceedings.

The legal action comes after the government refused to hand over some of Mr Johnson's WhatsApp messages to the inquiry, arguing that the material was of "private" and "personal" nature.

Mr Johnson, however, decided to bypass the Cabinet Office and hand over the unredacted messages direct to the inquiry.

The messages refer to discussions from before May 2021 and are likely to relate to the COVID-19 lockdowns ordered in 2020.

Which other countries have launched a COVID Inquiry?

Sweden's COVID commission, in a final 1,700-page report in February 2022, said the country's broad policy was "fundamentally correct" but that it should have shut venues and taken other, tougher measures earlier in the pandemic.

The country shunned lockdowns and masks and left schools, restaurants and businesses open while telling people to socially distance and maintain good hygiene.

In France, an appeals court threw out a judicial investigation into alleged negligence by former health minister Agnes Buzyn in her handling of the pandemic.

The French government's response during the first months of the pandemic came under fire from the public, with accusations Ms Buzyn had put people's lives at risk by not adequately communicating the dangers of the virus.

In Italy, former prime minister Giuseppe Conte, former health minister Roberto Speranza and 17 others are under investigation over the government's response to the pandemic.

In the US, a bipartisan group of senators tried to put together a COVID-19 commission to look into the origins of the virus and the national readiness.

It hasn't been able to get off the ground due to disagreements and a lack of support from the Biden administration.