Former British prime minister Boris Johnson was "dismissive of disaster" and labelled long COVID as "bollocks" in 2020, the UK COVID-19 Inquiry has been told.

The Bereaved Families for Justice group said there was a "leadership void" in early days of the crisis and accused Johnson of "cavalier" public messaging just weeks before the first lockdown.

Meanwhile, long COVID groups said he dismissed the condition as "bollocks" and "Gulf War Syndrome stuff" in October 2020.

The loss of these messages is a "remarkable and unfortunate coincidence" Peter Weatherby KC, for COVID-19 Bereaved Families for Justice, told the inquiry.

Speaking on the first day of the second module on Tuesday, Weatherby called for experts to examine the phone to see whether the messages could be retrieved "and whether they might have been deleted".

"Mr Johnson claims that although he's downloaded the phone, the WhatsApp messaging from the crucial period of the January 31 to June 7 2020 are unrecoverable," Weatherby said.

"A remarkable and unfortunate coincidence, we would say.

"We would urge the inquiry to commission experts to see why those messages can't be retrieved and whether they may have been deleted."

Weatherby said Johnson "failed to take the emerging threat seriously" as he called on the inquiry to consider "whether vital time to form a contingency plan and to act was squandered" and that key preparations may not have taken place "because part of the Government was in denial, and others had a false view of its own preparedness".

Meanwhile, Anthony Metzer KC, speaking on behalf of Long COVID Kids, Long COVID SOS and Long COVID Support, told the inquiry that Johnson initially "denied the truth of the suffering" of long COVID patients.

"In October 2020, while the Department of Health and Social Care was publishing guidance on long COVID and called for recognition and support for people with long COVID, then-prime minister Boris Johnson scrawled in capitals that long COVID was 'bollocks'.

"Mr Johnson has admitted in his witness statement that he didn't believe long COVID truly existed, dismissing it as 'Gulf War Syndrome stuff'."

"The inquiry will be concerned to probe how the former prime minister could possibly hold this view in October 2020.

"It is perhaps noticeable that the former prime minister now accepts that long COVID is a serious health condition, but does not say when he changed his mind.

"Adults and children were and still are suffering from debilitating, painful and terrifying symptoms for months and now years after infection, and yet Mr Johnson denied the truth of their suffering.

"The UK's senior most decision-makers were dismissing, diminishing and disbelieving the very existence and risk of long COVID."

The inquiry also heard a Cobra meeting was briefed on COVID-19 on January 29 but Johnson was not present.