Keir Starmer has hit out at the "ghoulish spectacle" of Tory politicians writing books portraying them as Covid "heroes".
The apparent swipe at Matt Hancock comes as the ex-Health Secretary denied claims he ignored advice on care home testing in a cache of leaked WhatsApps.
The messages were shared with The Telegraph by journalist Isabel Oakeshott, who worked with the former Cabinet minister on his Pandemic Diaries memoir.
Published in 2022 - before the public inquiry kicked off - Mr Hancock's book details discussions at the heart of Government during the Covid crisis.
Speaking at Prime Minister's Questions on Wednesday, the Labour leader said "there are too many messages and too many unknowns", regarding the leak.
But he added: "Families across the country will look at this and the sight of political writing books portraying themselves as heroes or selectively leaking messages, (it) will be an insulting and ghoulish spectacle for them".
Mr Starmer also called on Rishi Sunak to ensure the Covid public inquiry had the resources needed in order to report by the end of 2023.
He said the inquiry, which has been given the power to compel ministers to give evidence, said it had already cost taxpayers £85million.
"So can the Prime Minister assure the House no more delays, that the inquiry will have whatever support it needs to report by the end of this year?"
The PM stressed there was a legal process to follow, that the inquiry was independent, and it was important to "let them get on and do their job".
"Rather than comment on piecemeal bits of information, I am sure he will agree with me the right way for these things to be looked at is the Covid inquiry."
In an urgent question following PMQs, Labour's Liz Kendall told MPs: "The families of the 43,000 care home residents who lost their lives will be appalled by the former Health Secretary attempting to rewrite history, attempts that will turn to ashes along with his TV career.
"We need more humility and less celebrity from the Member for West Suffolk (Mr Suffolk), and above all we need answers."
She said: "Throughout the Covid pandemic ministers repeatedly claimed they threw a protective ring around England's care homes and always followed the scientific advice. But WhatsApp messages revealed in today's Telegraph reveal that nothing could be further from the truth."
Ms Kendall said she had repeatedly raised concerns about lack of testing in care homes, telling the Commons that 17,678 care home residents had died in the gap between Prof Chris Whitty's advice and the rollout of testing.
In response Tory social care minister Helen Whately said she was "shocked and disappointed" by the "tone" Ms Kendall had taken.
She claimed that the outrage followed the release of "selective snippets" of WhatsApp messages.
"The government followed the expert public health available at the time. We had the capacity to test just 3,000 cases a day in mid-March and I'm sure colleagues will understand why the health advice was to prioritise those on our NHS frontlines and indeed the testing of people in hospitals and indeed in care homes with symptoms...
"As we dramatically ramped up testing capacity we also adjusted that prioritisation in line with the public health advice and the capacity."
Ms Whately branded the messages under scrutiny as "very selective" and said an email sent at the same time clarified that capacity wasn't available at the time.
She told MPs: "While there were discussions and debates between Ministers and between colleagues which took place in part on WhatsApp there were clearly meetings and conversations in other forums in which advice was given and decisions made. A huge quantity of that is with the Public Inquiry.
"I can say that a meeting to discuss the implementation on the advice on testing was not reference in the WhatsApp messages that she was talking about, but for instance there was an email following exactly this exhange that said we can press straight away with hospitals testing patients going into care homes and we should aspire to as soon as capacity allows and we've worked out an operational way of delivering this that everyone going into a care home from the community could be tested.
"It's very selective information that she's basing her comments on."
Ms Whately said the government "strained every sinew" to protect care homes.
Ms Whately did not say when challenged how many, if any, ministers received priority Covid tests at the start of the pandemic - but she said leaked messages show she tried to use the public system.
Liberal Democrat MP Daisy Cooper asked: "The leaked WhatsApp messages from (former health secretary Matt Hancock) show that despite a shortage in Covid tests in September 2020, one of the minister's advisors sent a test to (Conservative former minister Jacob Rees-Mogg's) home by courier.
"This is yet more evidence that it's one rule for Conservative ministers and another for everyone else. So can the minister please inform the House: how many other Government ministers, Conservative MPs and their families, received priority tests during the pandemic when there was a shortage of tests?"
Ms Whately said: "Much though it's a difficult thing for me as a minister to see WhatsApp messages from me, in fact, in the pages of the newspaper, if she has read those she will see that I was seeking a test for a member of my family and using exactly the test app as everybody else to try and get access to a test that was needed."
Mr Hancock denied what was called the “distorted account” with a spokesman alleging the leaked messages have been “spun to fit an anti-lockdown agenda”.
He is said to be "considering all options" in response to the leak, with a source close to him saying: "She's [Ms Oakeshott] broken a legal NDA (non-disclosure agreement). Her behaviour is outrageous."
The spokesman said "instead of spinning and leaks we need the full, comprehensive inquiry".
