Video report by ITV News Health Editor Emily Morgan
Baroness Harding has been appointed the interim leader of new health agency, the National Institute for Health Protection, which is replacing Public Health England.
But the Tory peer's promotion has caused widespread anger among health experts and MPs who have questioned her credentials.
Health Secretary Matt Hancock defended Baroness Harding's promotion, saying she has a "combination of experience externally and experience in the NHS.
"She has been running NHS Test and Trace and building that from scratch into what is now one of the biggest testing and diagnostics organisations in the world," he said.
NHS Test and Trace has been widely criticised under her leadership, with it consistently failing to reach thousands of people potentially carrying coronavirus.
Matt Hancock defends Baroness Dido Harding's promotion:
The system - which has been blighted with failings since it was set up, including its abandoned app - has often been described by opponents as "not good enough" and ministers have admitted it "needs improving".
Since its inception, the programme - which aims to instruct self-isolation for people who may have been in close contact with the virus - has been unable to reach around 18.5% (48,625) of close contacts.
Aside from her experience in the NHS, Mr Hancock said Baroness Harding has "excellent experience externally, where she has run very large organisations".
She was previously the chief executive of telecoms company TalkTalk, where she twice won the Daily Mail wooden spoon award for the firm having the worst customer service in the UK.
The 52-year-old was also running TalkTalk when it fell victim to a cyber-attack which affected tens of thousands of its customers.Despite this, Mr Hancock said "her leadership will be vital" in driving forward the new health agency.
Many on social media criticised her appointment, saying it showed nepotism within the Tory party.
Baroness Harding was given a seat in the House of Lords in 2014 by her friend and then-PM David Cameron and is married to Tory MP John Penrose.
Liberal Democrat leadership contender Layla Moran said the appointment was "appalling" and said it is "undermining the reputation of this new agency before it has even been launched".
From today, Public Health England and NHS Test and Trace will merge but the National Institute for Health Protection will not be formalised until spring 2021.
Mr Hancock said he had “every confidence” that the new organisation will be “world-renowned”.
Mr Hancock said the National Institute for Health Protection will combine the existing “talent and science infrastructure” with NHS Test and Trace and the work of the Joint Biosecurity Centre.
He said the new organisation will have a single mission of “protecting people from external threats to this country’s health”.
Baroness Harding said the changes are "designed to strengthen our response, and to radically ramp up our fight against this disease, whilst also protecting PHE’s essential work beyond Covid that is so important for the nation’s health".
Announcing her appointment at the Policy Exchange think tank, Health Secretary Hancock said Baroness Harding "will establish the NIHP and undertake the global search for its future leadership".
“I have no doubt that under Baroness Harding we will found the NIHP as a thriving, mission-driven organisation.
“We have a common mission, the greatest mission of any of our working lives, and we have no time to lose in building the institution of the future.”
The new agency will "start work immediately" to "advance the country’s response to the Covid-19 pandemic", said the health secretary.
The responsibilities of the NIHP will include:
NIHP Local Health Protection Teams to deal with infections and other threats
Support and resources for local authorities to manage local outbreaks;
The Covid-19 Testing Programme
The Joint Biosecurity Centre
Emergency response and preparedness to deal with the most severe incidents at national and local level
Research and reference laboratories and associated services
Specialist epidemiology and surveillance of all infectious diseases
The Centre for Radiation, Chemical and Environmental Hazards
Global health security
Providing specialistic scientific advice on immunisation and countermeasures.
Duncan Selbie, the outgoing PHE Chief Executive, will be taking on a role as a senior advisor to the Department of Health and Social Care on global and public health.