The coronavirus public inquiry has asked to see Boris Johnson’s WhatsApp messages when he was Prime Minister, alongside communications with other senior officials.

Counsel for the inquiry, Hugo Keith KC, said thousands of documents had been requested to inform the inquiry, and gave the Cabinet Office as an example.

“We have sought agendas, minutes and other documents associated with the core decision-making forum such as Cabinet meetings, Cobra meetings and ministerial implementation groups,” he said.

“We’ve asked for ministerial submissions, Number 10 daily briefing documents, records of written and oral advice to ministers and details of internal communications including a WhatsApp group, which included the Prime Minister, Number 10 and other senior officials.”

Module two will scrutinise political decisions and actions in relation to the pandemic, between early January 2020 and February 2022, when remaining Covid-19 restrictions were lifted.

The inquiry has requested evidence from the Cabinet Office, Foreign Commonwealth and Development office, the Department of Health and Social Care, the Office of the Chief Medical Officer, the Government Office of Science, the Scientific Advisory Group for Emergencies (Sage), Independence Sage, the Home Office, Treasury, Departments for Education, Transport, Levelling Up, Work and Pensions, Business, Energy and Industrial Strategy, the UK Health Security Agency and NHS England.

Initial responses from Government departments indicated tens of millions of documents could potentially be relevant to the module’s overall theme, with reviews of documents in the Cabinet Office alone estimated as likely to take over three years.

Hugo Keith KC, counsel for the inquiry, said the inquiry is instead taking a “targeted approach”, seeking documents relevant to the key narrative events, people and decisions covered by the second module.

And he said the director general of propriety and ethics in the Cabinet Office has written to Government departments reiterating the need to retain documents relevant to the probe.

Pete Weatherby KC, representing bereaved families, said a targeted approach gives “significant latitude” to those who are subject to investigation “to be the ones that actually determine – rather than the inquiry in the first place at least – what is disclosed”.

He added that families would urge the inquiry “to keep a very open mind of people who may have reason to try to rein in their own disclosure”.

Shanthi Sivakumaran, representing groups for disabled people and people with long Covid, called for the inquiry to disclose a list of the key narrative events, people and decisions referred to by Mr Keith.

It should also disclose statements from bodies which provide requested evidence, explaining their review of documents, she said.

These should say if any documents have been deleted before or after steps were taken to retain potentially relevant material, she added.

Earlier, Mr Keith said module two would examine whether lives could have been saved by earlier lockdowns.

In his opening address, he said the crisis placed “extraordinary levels of strain” on the UK’s health, care, financial and educational systems and businesses, on top of individual bereavements.

He said: “The disease has caused widespread and long-term physical and mental illness, grief and untold misery.

“Its impact will be felt worldwide, including in the United Kingdom, for decades to come.”

Inquiry chairwoman Baroness Heather Hallett will examine the effectiveness of mandatory lockdowns in controlling the spread of coronavirus, the inquiry was told.

This will include “the relationship between the timeliness and the length of the lockdown, and the trajectory of the disease”, Mr Keith said.

He continued: “How were economic and societal impacts, including the impact on physical health, healthcare provision, mental health, education and societal wellbeing, assessed and weighed in the balance?

“And perhaps, my lady, the single most important question: is it possible to say what the likely effects of earlier or different decisions to intervene would have been? The counterfactual proposition.

“Bluntly, would lives have been saved if the lockdowns had been imposed earlier or differently?”

Questions will also be asked about the role of Sage, including whether any lessons may be learned from the “structures in place in other countries for the provision of scientific advice to policymakers”.

Mr Keith added: “Was the system of government medical and scientific advisers effectively utilised? How effective was the decision-making system under which the Prime Minister and other ministers acted on the advice and recommendations of the relevant bodies and advisers? Did the system allow properly for timely political decision-making?”

He said further questions would be asked about whether committees were working with relevant and accurate data.

“How effectively was data distributed through the Government? How reliable was the infectious disease data modelling? Did the data modelling cover the right eventualities? Was there an over-reliance on epidemiological modelling or mathematical modelling? Was there an over-reliance on influenza epidemiology and data modelling?”

Around 200 scientists, including all those involved in the Sage group and others in the Independent Sage group, have been asked to give evidence about the effectiveness of the pandemic response.

The probe also heard that 39 individuals, groups and institutions have been granted core participant status for the second module, enabling them to access relevant evidence and suggest lines of questioning.

Mr Keith said the pandemic “reached out and affected almost every person” but its impact was not equally felt.

He welcomed the inclusion of bodies representing children, older people, disabled people, domestic abuse victims, those with chronic mental and physical health needs, members of ethnic minority communities and people with long Covid.

They also include bereaved groups, Government departments, unions, NHS England, and Imperial College, where Professor Neil Ferguson, the academic whose data was instrumental to the UK going into lockdown in March 2020, works.

A further preliminary hearing for the module will take place in early 2023, with public hearings starting in the summer, scheduled for around eight weeks.