Downing Street has confirmed that Sir Keir Starmer uses a disappearing message feature on WhatsApp, meaning conversations between the prime minister and Peter Mandelson may have been deleted and lost.No 10 confirmed on Tuesday that the prime minister has the controversial feature turned on, but insisted Sir Keir used it in line with guidance stating they are permitted so long as it “does not impact record keeping or transparency responsibilities”. But the admission has raised questions about the extent of messages missing between Sir Keir and the former Labour peer in the latest tranche of the Mandelson files, released on Monday.The prime minister’s official spokesman said: “The prime minister does use disappearing messages. As you'll be aware some ministers do use that function in line with the government's advice on non-corporate communications channels.”WhatsApp allows users to set messages to automatically vanish after 24 hours, 7 days, or 90 days, meaning past exchanges between the prime minister and Mandelson would now be unrecoverable.Sir Keir Starmer’s decision to appoint Lord Peter Mandelson as ambassador to the US has had major repercussions (Carl Court/PA) (PA Wire)There was only one page of messages between Sir Keir and Mandelson - sent on iMessage rather than WhatsApp - included in Tuesday’s release.The disgraced peer offered advice during the 2024 general election campaign and Sir Keir’s first days in office, and also set up a meeting between John Major and the prime minister.On June 27 2024, Mandelson texted Sir Keir, advising he focuses on a message of “what unites us” in the final week of the campaign. Sir Keir replied: “Thanks Peter. That theme of unite not division is very powerful. People are fed up with politics treading too heavily on their lives. How did Bury seem to you?”On the 17 July, weeks after Sir Keir became prime minister, Mandelson texted him to say he had “got off to a flying start”, and advised him to invite John Major for a chat after he had dinner with him.There was only one page of messages between Sir Keir and Mandelson - sent on iMessage rather than WhatsApp - included in Tuesday’s release. (Reuters)Sir Keir replied: “Thanks Peter. Its so good to be getting on with the job of governing. A million times better than opposition - you know that! I’ll reach out to John M, he’s a very thoughtful man. See you soon I hope.”Downing Street said that, although disappearing messages could be used in line with government guidance, lessons on record keeping would be learned going forward.The spokesman added: “The prime minister has fully complied with humble address by providing all information he holds.”The government is facing humiliation after it released a second tranche of more than 1,000 pages of documents related to Mandelson’s ill-chosen appointment as US ambassador.The documents - which included thousands of previously private messages between figures at the heart of government and Mandelson - laid bare Mandelson’s damning opinion of the government, as he warned that Sir Keir’s Downing Street operation is “beleaguered and bereft”.The prime minister’s spokesman insisted on Tuesday that Sir Keir remains confident in Mr McFadden. (PA)Mandelson himself “declined to comply” with a request to hand over his personal phone and allow the government to publish WhatsApp messages and other information related to his appointment, the documents showed.Other messages revealed in-fighting within the Labour Party, with work and pensions minister Pat McFadden having criticised Labour MPs in messages to Mandelson.Mr McFadden criticised the Parliamentary Labour Party, telling Lord Mandelson: “Every meeting I have is 'who can we tax in order to pay benefits to others'. They’re asking the wrong questions.”But the prime minister’s spokesman insisted on Tuesday that Sir Keir remains confident in Mr McFadden.