The U.K. Government released a vast trove of documents relating to Peter Mandelson’s appointment as U.S. Ambassador, in a move that threatens to cause fresh damage to Keir Starmer’s faltering premiership.

More than 1,500 pages of documentation were published on the British government’s website just after 2 p.m. local time. They include emails, text messages and other exchanges between government ministers, aides and Mr. Mandelson in the run-up to his appointment as U.S. Envoy, a post he held from February to September 2025.

The release resurfaces a saga that has weakened and embarrassed Mr. Starmer over the nine months since Bloomberg News exposed the extent of Mr. Mandelson’s ties with the late pedophile financier Jeffrey Epstein. An earlier tranche of documents in March showed official vetting of Mr. Mandelson had warned of “reputational risks” over Mr. Mandelson’s Epstein ties.

The scale of Monday’s (June 1, 2026) drop — described by the government as one of the biggest-ever Parliamentary publications — means its full impact on Mr. Starmer won’t immediately be known. 

But the Prime Minister has already suffered months-long blowback from both opposition parties and his own Labour MPs concerning the judgment he showed in appointing Mr. Mandelson, given the former Labour grandee’s history of resigning in disgrace from past government roles and a penchant for political maneuvering that earned him the nickname “Prince of Darkness.”

The scandal has already led to the departure of Mr. Starmer’s chief of staff, Morgan McSweeney, who quit in February citing his advice to the premier to appoint Mr. Mandelson. He was followed out of Downing Street by Tim Allan, who had been director of communications. 

The disclosure of information relating to the former envoy was forced on the government in February by the main opposition Conservative Party, using an arcane parliamentary procedure known as a humble address. Under its terms, the government must disclose communications between Mr. Mandelson and Ministers and officials for the six months prior to his appointment as Ambassador, and throughout his seven-month tenure. 

That has been complicated by the police investigation into the former envoy, with officers requesting that some information be withheld so as not to prejudice their probe.

Ahead of the publication on Monday (June 1, 2026), Mr. Starmer’s spokesman, Tom Wells. told reporters the task had involved every government department, resulting in the largest ever response to a humble address.

“It represents thousands of hours of work from officials across the government to deliver an unprecedented piece of government transparency,” Mr. Wells said. “Material of a party-political nature will be included in the publication, which is contrary to usual practice and precedent, in order to demonstrate the maximum possible transparency. A number of documents have also been declassified to enable publication.”

Mr. Starmer’s premiership is hanging in the balance not even two years on from his landslide general election victory in July 2024. His government quickly lost popularity with voters amid a series of scandals and missteps, not least the appointment of Mandelson himself.

Heavy losses at a set of local elections in May led to more than 90 Labour MPs calling for Mr. Starmer to resign. Andy Burnham, the Greater Manchester mayor, is widely expected to launch a leadership challenge against Mr. Starmer this summer if he can first win a parliamentary special election in northwest England that’s scheduled for June 18.

Since Bloomberg’s investigation into Mr. Mandelson’s Epstein ties, which centered on information published by the U.S. Department of Justice relating to the disgraced financier, further revelations in the Epstein files have led to a police investigation and plunged Mr. Starmer’s administration into political chaos as the premier struggled to defend his handling of the appointment. Mr. Mandelson has denied any wrongdoing.