Ministers have been accused of trying to deflect attention from their own failings during the Covid-19 pandemic by planning to scrap Public Health England before a potential second wave.

It emerged on Sunday that PHE is set to be merged with NHS Test and Trace to form a new body called the National Institute for Health Protection.

Downing Street has been frustrated for months by PHE’s limited capacity to test samples for coronavirus and trace contacts of those infected, and the way it counts Covid-related deaths.

Its potential abolition has been an open secret in Whitehall for months. Boris Johnson had the agency in mind when he referred in June to how parts of government had been “sluggish” in their response when the pandemic struck in March.

But critics said ministers were scapegoating PHE for failures by central government and NHS Test and Trace, and the reorganisation was badly timed given the continuing threat posed by the virus.

Prof John Ashton, a former regional director of public health, said of the plan: “It completely fails to understand the issue and would compound the problem. It is more distraction and blame shifting when what is needed is reform, strengthening and decentralisation.”

Referring to the potential appointment of the NHS Test and Trace chief executive, Dido Harding, as the boss of the new institute, Ashton added: “You don’t do this in the middle of a crisis, and certainly not put Dido in charge when she has been such a disaster with test and trace.” Harding is also chair of NHS Improvement, an NHS regulator.

The Liberal Democrats’ health spokesperson, Munira Wilson, said: “With the coronavirus crisis taking its toll on the daily lives of people up and down the country, this announcement will go down like a bucket of cold sick.

“Be in no doubt, ministers are attempting to deflect responsibility for their shambolic management of the pandemic with a bureaucratic reorganisation. Instead of rearranging the deckchairs, they should be learning lessons ahead of a possible second wave.”

PHE was set up in 2013 as part of an overhaul of the NHS in England pushed through by Andrew Lansley, the health secretary in the coalition government. It is an agency of the Department of Health and Social Care (DHSC).

Under that shake-up, responsibility for public health was taken from the NHS and handed to local councils, despite public health experts warning against the move.

A senior director of public health, who did not want to be named, told the Guardian: “It is not helpful to reorganise the country’s public health system in the middle of a pandemic. The main failings have not been PHE’s but in national testing capacity and in the private-sector test-and-trace system [in which Serco is centrally involved]. National test and trace outsourced to the private sector is a major failing of system response capacity, not PHE.”

The plan was revealed by the Sunday Telegraph. An unnamed minister told the paper that the new institute would increase capacity to respond to the pandemic in a way that PHE, with its limited resources, had been unable to do.

“We want to bring together the science and the scale in one new body so we can do all we can to stop a second coronavirus spike this autumn,” the minister was quoted as saying. “The National Institute for Health Protection’s goal will be simple: to ensure that Britain is one of the best-equipped countries in the world to fight the pandemic.”

The change will take until next year to formally complete but will take effect from September, and the new body will have tens of thousands of staff, according to the Sunday Telegraph. PHE’s budget was cut in recent years as a result of austerity.

The paper said Downing Street had been unimpressed with the PHE chief executive Duncan Selbie’s performance in recent months. His future is unclear.

Ashton said flaws in the government’s response to the pandemic owed in part to the fact that none of its key health advisers at the start had a background in public health.

“The big problem here has been having politicians who don’t understand public health advised by people who don’t understand hands-on local public health because they are too remote and academic and have never actually done it,” he said.

“Duncan Selbie is a hospital manager with no public health knowledge or experience, and there has been nobody on Sage who has been a local director of public health. Only one of the four chief medical officers is properly public health-trained – Frank Atherton in Wales.”

In a statement, Selbie said criticism of PHE over its testing of samples early in the pandemic was “based on a misunderstanding” of its role and capacity.

“The UK had no national testing capabilities other than in the NHS at the outset of the pandemic. PHE does not do mass diagnostic testing,” he said. “We operate national reference and research laboratories focused on novel and dangerous pathogens, and it was never at any stage our role to set the national testing strategy for the coronavirus endemic. This responsibility rested with DHSC.”