Rishi Sunak has been accused of being "slippery" in the row over whether the government will hand over Boris Johnson's WhatsApp messages and other documents to the COVID inquiry.
Labour's shadow health secretary Wes Streeting said the prime minister should "comply with the inquiry and do it today".
Mr Streeting told broadcasters: "I think the prime minister looks really slippery today. He says he wants the government to co-operate with the inquiry but the government has been withholding information the inquiry has asked for.
"One minute the government says the messages they have are immaterial; the next minute they're saying they don't exist. Which is it?"
Inquiry chair Lady Hallett had ordered the government to hand over the messages - alongside diary entries and notes - by 4pm on Tuesday 30 May.
The deadline has now been set for 4pm on Thursday 1 June. The Cabinet Office asked for an extension to Monday 5 June as they do not have access to Mr Johnson's messages or notebooks, but this was rejected.
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What is the COVID inquiry asking for?
Unredacted messages sent and received by Boris Johnson between 1 January 2020 and 24 February 2022.
Unredacted diaries for Mr Johnson between 1 January 2020 and 24 February 2022
Copies of 24 unredacted notebooks filled in by Mr Johnson between 1 January 2020 and 24 February 2022
Unredacted messages sent and received by adviser Henry Cook between 1 January 2020 and 24 February 2022.
The inquiry wants messages - even from group chats - about the government response to COVID, as well as contact with a list of certain experts, ministers, civil servants and advisers
This is despite saying in their original appeal against the order that there was "unambiguously irrelevant" material in the redacted parts of messages sent to the inquiry.
When the Cabinet Office lodged the appeal on 15 May, it said Mr Johnson's WhatsApp messages had not yet been received by the government.
A spokesman for the former prime minister said today that he had "no objection" to sending the material to the inquiry.
Mr Johnson has written to the Cabinet Office to demand the government requests in writing access to his messages and notes - which he says has not happened yet.
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PM: Govt 'cooperating with COVID inquiry'
Sources close to Mr Johnson say Cabinet Office officials have visited his office in person to examine notebooks within the past few weeks.
If the government does not abide by the new deadline on Thursday, Lady Hallett has ordered that a statement be sent by a "senior civil servant" confirming the Cabinet Office does not have the requested information, as well as a chronology of the government's contacts with Mr Johnson about the requests and whether the government has ever had the data.
Breaking a section 21 order could see the government face criminal proceedings, and there is also potential for a court battle over whether the information should be passed to the inquiry.
Speaking shortly before the inquiry's announcement, Mr Sunak said the "government is carefully considering its position, but it is confident in the approach that it's taking".
But Mr Streeting said the prime minister's "slipperiness" gave "the impression of someone who is not fully committed to transparency, openness, accountability".
Asked whether he was concerned about a potential "cover up", Mr Streeting said: "I think the fact the prime minister looks so slippery today will be a cause of deep anxiety to people who are following the inquiry closely - not least those families who have suffered bereavement and just want some honesty and some answers."
The battle between the parties centres on messages Mr Johnson sent and received, as well as his diaries and his notebooks from during the pandemic.
Image:Baroness Hallett opens preliminary hearing for COVID-19 inquiry
Image:Baroness Hallett opens preliminary hearing for COVID-19 inquiry
Lady Hallett made an order under section 21 of the Inquiries Act 2005 for the material to be handed over by the Cabinet Office.
Messages to and from former adviser Henry Cook were also included in the legal action.
It is this order which has now been extended.
Lady Hallett highlighted in her explanation that the Cabinet Office redacted material about the policing of Sarah Everard protests during the period of restrictions - something she said was "not a promising start".
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New deadline for ex-PM's COVID messages
She later obtained the messages in full.
She also identified communications - which have still only been seen in their redacted form - that she considers are "in fact relevant to my investigation".
Labour's deputy leader, Angela Rayner, said: "It now appears that vital evidence has gone missing. It must be found and handed over as requested if the whiff of a cover-up is to be avoided and bereaved families are to get the answers they deserve."
Daisy Cooper, the Liberal Democrats' deputy leader, added: "The public has waited long enough already to get the truth. The inquiry's work mustn't be delayed any longer because of endless chaos in the Conservative Party."
