During his appearance at the COVID inquiry on Wednesday, four people were removed from the public gallery after holding up pictures, along with the words: "The dead can't hear your apologies."

Mr Johnson told the inquiry: "I am deeply sorry for the pain and loss and suffering."

The former prime minister went on to say he hoped the probe was able to "get answers to those very difficult questions" victims and their families were "rightly asking".

Boris Johnson COVID evidence live: Former PM apologises to victims as he begins marathon evidence session at inquiry

During the mammoth evidence session that will continue on Thursday, the inquiry also heard from Mr Johnson that:

• The government "underestimated the scale and pace of challenge" from COVID - thinking the peak would come in May or June;

• The tone of private WhatsApp exchanges was a "reflection of the agony" the country was going through;

• A denial the then prime minister was on holiday over the half-term break in February 2020 - as claimed by former aide Dominic Cummings

• He "can't say" whether he would have "gone earlier" in ordering the first lockdown;

• He took "full responsibility" for the decisions made;

• And he offered an apology to sufferers of Long COVID, having described the condition as "b*****ks" in 2021.

Watch a Sky News special on Johnson's day of evidence at 9pm

Mr Johnson was speaking on the first day of his appearance at the official COVID inquiry he set up in order to learn the lessons of the pandemic for the future.

He is the probe's most highly anticipated witness and follows on from fellow politicians including former health secretary Matt Hancock, former deputy prime minister Dominic Raab and Levelling Up Secretary Michael Gove.

The inquiry, which is now examining decision-making and political governance, began with Baroness Hallett raising issue with briefings ahead of Mr Johnson's appearance, arguing that a leak "undermines the inquiry's ability to do its job fairly, effectively and independently".

Read more: Key points so far as Boris Johnson gives evidence to COVID inquiry

'Were there things that we should have done differently? Unquestionably'

The former prime minister told Hugo Keith KC, lead counsel for the inquiry, that "unquestionably" mistakes were made by his government during the pandemic, adding that he took "responsibility for all the decisions that we made".

Pressed on what he believed those to me, Mr Johnson cited communications and the different messaging coming from the different governments in the UK.

Mr Johnson also said he took responsibility for the speed of the government's response to the pandemic, the lockdown decisions and their timeliness, the circulation of the virus in the residential care sector and the Eat Out to Help Out scheme.

The ex-prime minister, who was ousted from Downing Street in the summer of 2022, said he acknowledged that "so many people suffered, so many people lost their lives".

But he said the government was "doing our best at the time, given what we knew, given the information I had available to me at the time, I think we did our level best".

Mr Keith KC then turned to questioning Mr Johnson on why he did not foresee the scale of destruction the the COVID pandemic would cause in early 2020, given that the inquiry had seen evidence to suggest others were concerned as early as February.

Mr Johnson admitted the wider government "underestimated" the threat posed by the virus, saying the "concept of a pandemic did not imply to the Whitehall mind the kind of utter disaster that COVID was to become".

He said in the "early days of March", government figures and officials "were all collectively underestimating how fast it had already spread in the UK" and thought the peak would be in May or June which turned out to be "totally wrong".

"I don't blame the scientists for that at all," he said.

"That was the feeling and it just turned out to be wrong."

Long COVID

Mr Johnson was also questioned about his remarks over Long COVID - a condition which, according to Oxford University, affected up to 10% of people who caught the virus.

Documents shown to the inquiry had scribbles alongside by the prime minister, referring to it as "b*****ks" and "Gulf War Syndrome stuff".

Mr Johnson said he realised the remarks had "caused hurt and offence", adding: "I regret very much using that language and should have thought about the possibility of future publication".

But he claimed he was trying to "get to the truth of the matter" and to get officials "to explain to me exactly what the syndrome was".

Missing WhatsApps

In the days leading up the inquiry there were reports anticipating Mr Johnson's apology and the fact that not all of his WhatsApps would be made available to the inquiry - with about 5,000 messages on his phone from January 30, 2020 to June 2020 missing.

Mr Johnson said he did not know the "exact reason" the messages had not been located, but said it was "something to do with the app going down and then coming up again, but somehow automatically erasing all the things between that date".

"Can I, for the avoidance of doubt, make it absolutely clear I haven't removed any WhatsApps from my phone and I've given you everything that I think you need," he said.

Read more:
Michael Gove apologises for pandemic 'errors'
Inquiry about 'scapegoating' senior govt figures - Johnson's sister

Government had 'challenging and competing characters'

Mr Keith told Mr Johnson that WhatsApp messages that have previously been shown to the inquiry "paint an appalling picture, not all the time but at times, of incompetence and disarray".

Mr Johnson argued that plenty of successful governments have "challenging and competing characters whose views about each other might not be fit to print but who get a lot done".

The former prime minister said the tone of the private messages was a "reflection of the agony" the country was going through.

"It was a very difficult, very challenging period," he said. "People were getting - as you can see from the WhatsApps - they were getting very frazzled because they were frustrated."