Richard Tice has predicted that Sir Keir Starmer "may not last until May" following an emergency debate on Lord Peter Mandelson.
Speaking to GB News, the Deputy Leader of Reform UK accused the Prime Minister of having "misled" Parliament following an "extraordinary" debate on the ex-Ambassador to the US.
During the debate, Labour MP Emily Thornberry revealed that Lord Mandelson was "not properly vetted" by the Foreign Office until after his appointment by Sir Keir.
Ms Thornberry told the House: "Mistakes can be made and obviously have been made, because while the shocking revelations of the last week were were not in the public domain in December, Lord Mendelson's relationship with Jeffrey Epstein was very widely known.
Richard Tice has claimed Labour has been left 'rocked and reeling' after an emergency debate on Lord Mandelson
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"And had my committee had the opportunity to question Lord Mandelson, I am confident that our members would have raised a range of questions."
Discussing the debate on GB News, Mr Tice stated: "It was a extraordinary three-hour debate, and I raised two issues.
"One is the Prime Minister's woeful political judgment, because he personally made the decision to appoint Lord Mandelson in the knowledge, with a two-page dossier summary, that he basically had links to a convicted paedophile.
"And then also I think he actually inadvertently misled the House of Commons last Wednesday, when he said that a full due process had been carried out during the appointment."
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Ministers held an emergency debate on Peter Mandelson in the Commons on Tuesday
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He added: "That is not true because he had made the appointment and announced it, as we now know before the whole vetting process properly started. So it was a pretty significant debate, very fiery, brilliantly led by David Davis MP.
"And I have to say, the Government minister was rocked and reeling all afternoon."
As host Tom Harwood analysed the debate and highlighted his surprise at how many Labour ministers "went for the jugular", Mr Tice declared it is because Lord Mandelson's actions are "indefensible".
He told Tom: "It's because what he has done is so totally indefensible. You can't defend being the 'best pal' of a convicted paedophile or that recommending to the paedophile to use his jail term as an 'opportunity'. That was the advice from Lord Mandelson. I mean, it doesn't get any worse.
Mr Tice told GB News that Labour has been left 'rocked and reeling' following the emergency debate on Lord Mandelson
|GB NEWS
"He has been utterly humiliated on the international stage ahead of the visit by President Trump, and I think the Prime Minister is very glad there's not Prime Minister's Questions tomorrow, because he is on very thin ice. And the chat in the House of Commons is that the Prime Minister may not last until May."
Pressed by Tom on whether Reform UK's announcement on Monday of Danny Kruger's defection has "slowed pressure" on Sir Keir, Mr Tice disagreed and declared the party is "parking tanks" on both Labour and the Tories.
He concluded: "We're doubling down. We were putting massive pressure on the Conservative Party, and everyone knows there's huge pressure on the Labour Party.
"So basically we're just parking our tanks on both of the two main parties lawns pretty successfully, I would suggest."