Long-awaited documents published by the government have revealed messages between Lord Mandelson and ministers strongly criticising the prime minister, No 10 and Labour MPs.
The 1,500 pages cover communications about the appointment of Lord Mandelson as the UK's ambassador to the US - a role he was later sacked from due to his links to convicted sex offender Jeffrey Epstein.
In one message, Lord Mandelson describes No 10 as "beleaguered and bereft" and in need of a "complete revamp".
In another exchange, minister Pat McFadden appears to complain about Labour backbenchers saying: "Every meeting I have is 'who can we tax in order to pay benefits to others'. They're asking the wrong questions."
At the time, McFadden was a Cabinet Office minister, however he has since become the work and pensions secretary.
A spokesperson for McFadden said: "Pat has said publicly many times that the question we should ask is not what are you entitled to, but how can we change your life?
"That has been his whole approach as work and pensions secretary, focusing on how we best spread work and opportunities to young people in particular, rather than writing them off as the previous government did."
Responding to the documents, Conservative leader Kemi Badenoch said: "Pat McFadden has said in private what he and the prime minister deny in public.
"As I've said repeatedly, Labour MPs don't understand where money comes from. They think our taxes are their money to spend, rather than the result of the hard work of the people in our country who deserve so much better."
In late June 2025, Lord Mandelson and McFadden exchanged messages about the government's welfare legislation, which aimed to cut £5bn from the benefits bill by 2030.
A major rebellion by Labour MPs forced the government to massively water down its proposals.
In the build-up to the vote on the bill, McFadden says MPs were "not moving".
Lord Mandelson replies that the government could lose the vote adding: "I am not sure that Keir survives that."
McFadden says: "He is meeting the ringleaders today. I think it's very bad. Defeat, pull bill or gut it all destroy his authority" adding in a follow-up message "Keir's authority."
"Yes, I am afraid so," says Lord Mandelson.
A few weeks later the two men appear to discuss Morgan McSweeney, who was the prime minister's chief of staff at the time.
Lord Mandelson says: "He [McSweeney] seemed to be saying to me last night that he has no faith in Keir's ability to change No 10 and that he needs to prioritize winning majority support in PLP instead."
He later adds: "I am slightly losing faith in all this."
Three days later Lord Mandelson asks McFadden: "How is No 10 now in your view?"
"Not good," he replies adding that No 10 advisers "came to see me the other day. I don't think they know what they want."
"And if they pull me in I'm not sure what to ask for to make it work."
Lord Mandelson says: "If they don't explain what they want very clearly what is Keir supposed to do?
"Rubbish in, rubbish out. You need the sort of status and remit that I had with GB [Gordon Brown]."
On 30 July, reflecting on senior staff in No 10 Lord Mandelson says: "They don't work as a team, they are not led and none of them really know what Keir thinks or wants.
"In fact most of them don't think Keir knows what he wants".
He later describes Downing Street as "beleaguered and bereft" adding: "It requires complete revamp and infusion of purpose and confidence to get anywhere."
Around the same time, Lord Mandelson messages another minister, Torsten Bell, saying: "The government doesn't do policy, generally speaking, well enough. It all starts with policy".
Bell, now a Treasury minister, said: "Everyone seems to think it's someone else's job to get the policy right… which is very odd."
Lord Mandelson replied: "As the saying goes, rubbish in rubbish out…"
The prime minister announced he was picking Lord Mandelson to be his new ambassador on 20 December 2024.
In a handwritten note sent a month earlier, Lord Mandelson promised the then-Foreign Secretary David Lammy: "If you were minded to appoint me I would make sure you never regret it."
The government was forced to publish the documents, following a vote by MPs in Parliament earlier this year.
Speaking in the House of Commons on Monday, Cabinet Office minister Darren Jones told MPs it was "one of the largest government publications" and had cost his department more than £1m.
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