Lead counsel Hugo Keith KC read out the evidence on the first day of the second part of the inquiry on Tuesday, which focuses on political decision-making in Westminster between January 2020 and February 2022.

Mr Keith revealed WhatsApp messages between Boris Johnson, Dominic Cummings and others "portray a depressing picture of a toxic atmosphere" during the pandemic.

He said the messages also showed "factional infighting and internecine attacks on colleagues".

A significant number of WhatsApp and diary entries refer to Matt Hancock. The messages imply Mr Johnson and a number of officials and advisers held the then health secretary in low regard. In particular, on account of an apparent tendency "to use their words, get over-excited and then make stuff up".

'There is no lockdown plan'

Some of the evidence mentioned in the inquiry included:

• On 11 March 2020 Mr Hancock briefed the cabinet, saying "that without symptoms it was highly unlikely that [sic] someone was suffering from coronavirus".

• On 14 March 2020, Mr Cummings, the then prime minister's aide, sent a message to Mr Johnson saying: "You are going to have to lock down but there is no lockdown plan. It does not exist. SAGE haven't modelled it. The Department of Health and Social care don't have a plan."

• At a meeting on the 25 October 2020 an argument began before the prime minister - the proponents of one side of the argument said "to let it rip" rather than impose a second lockdown.

Advice was 'cherry-picked'

The inquiry also heard how Downing Street "rewrote" scientific advice on the two-metre social distancing rule.

In June 2020, Sir Patrick Vallance, the chief scientific adviser to Mr Johnson's government, expressed his dismay in his diary about changes made to a scientific review of social distancing, noting that the advice had been "cherry-picked", which he found "quite extraordinary".

During this period, the government was preparing to release new social distancing recommendations as part of the phased easing of lockdown measures on 23 June.

The government's guidance at the time recommended that individuals aim to maintain a two-metre distance from others but, when not feasible, follow a "one-metre plus" approach.

The inquiry was also told that in early March 2020, as the virus was spreading rampantly across the UK, a Number 10 aide wrote "we are f***ed" during a meeting of the government's scientific advisory committee, SAGE.

On 2 March, Mr Cummings sent a text message to Lee Cain, the director of communications, saying the prime minister "doesn't think it's a big deal. He doesn't think anything can be done" about the virus.

But just 11 days later, on 13 March, Mr Keith disclosed that a senior Cabinet Office official visited Number 10 and said: "I think this country is headed for disaster. I think we're going to kill thousands of people."

By the end of March 2020, there had been a total of 1,808 coronavirus-related deaths, and 25,150 confirmed cases of the virus.

Mr Johnson had also announced a raft of tough measures to tackle the pandemic, such as staying at home and away from others, closing non-essential shops and public spaces and stopping public gatherings.

'We've got big problems coming'

On the morning of the 12 March 2020, Mr Cummings sent a text to the prime minister saying: "We've got big problems coming. The Cabinet Office is terrifyingly s***. No plans. Totally behind the pace. We must announce today, not next week, 'If you feel ill with cold or flu, stay home'.

"Some around the system want a delay because they haven't done the work. We must force the pace. We are looking at 100 to 500,000 deaths between optimistic and pessimistic scenarios. You've got to chair the daily meetings in the Cabinet Room, not Cobra - because the Cobra system could not work; we could not get all the data in properly. It did not work for a kind of open thing."

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Sir Patrick's diary entries also indicated that he, along with chief medical officer Professor Sir Chris Whitty and other SAGE scientists, felt they were being used as a shield by some in the government to deflect blame for pandemic mistakes.

During the height of the COVID crisis in 2020, Sir Patrick sensed a growing sense of concern within Downing Street about SAGE, describing it as a "SAGE is in trouble vibe".

Bereaved families told they 'will not be ignored'

Meanwhile, bereaved families staging a silent protest outside the UK COVID Inquiry on Tuesday were told that they "will not be ignored" by Baroness Heather Hallett.

The families, some holding portraits of their deceased loved ones, claim that the ongoing investigation is overlooking the ways in which politicians and policymakers fell short in their duties to protect and support them.

Baroness Hallett, a former Court of Appeal judge who is leading the inquiry, told the hearing that Tuesday marked "another important milestone".

She revealed that the second phase of the inquiry, known as "module two," would focus on high-level governance and decision-making during the worst period of the pandemic.

"Some of those who suffered, and who continue to suffer, maintained a dignified presence outside the hearing centre this morning to remind us of why we are all here," she said.

"We will be hearing from some of them during the course of this module."

The inquiry is set to hear from Boris Johnson, his then Chancellor Rishi Sunak, Dominic Cummings, Matt Hancock, chief scientific and medical advisers, and others who had key roles to play in the decisions made by the UK government.