The UK's focus on Brexit seriously hindered the country's COVID-19 planning, according to the Covid-19 inquiry.
The inquiry, which is looking into the UK's resilience and preparedness, began its first public session on Tuesday.
The UK recorded over 128,500
Covid-19 deaths by mid-July 2021, and the current total number of deaths stands at just over 227,000.
The inquiry is chaired by a retired senior judge and is examining the country's handling of the pandemic.
However, some relatives of those who died in the pandemic have criticized the inquiry for not including them and say it will be a "farce" if they are not able to testify.
The UK government is refusing to release unredacted communications related to the lockdowns in 2020, which are likely to be central to an inquiry into government decision-making during the pandemic.
A High Court judge is set to rule on the request at the end of June.
Leading epidemiologists Jimmy Whitworth and Charlotte Hammer will give evidence to the inquiry on Wednesday.
Public inquiries in the UK investigate matters of public concern, establishing facts and making recommendations, but do not rule on civil or criminal liability.
Later phases of the inquiry will focus on the health service,
vaccines, and the care sector.
The inquiry is expected to conclude by mid-2026.