The Liberal Democrats have urged the UK’s financial regulator to immediately investigate Peter Mandelson, saying his apparent decision to leak highly confidential government information to the disgraced financier Jeffrey Epstein may have led to insider trading.

In a letter to Nikhil Rathi, the chief executive of the Financial Conduct Authority (FCA), Daisy Cooper, the MP for St Albans and the Lib Dems’ deputy leader, said it was “crucial” to determine whether Mandelson or those he shared information with had profited from accessing “market-sensitive and confidential material” in the aftermath of the 2008 financial crisis.

“The sharing of confidential information with a private financier could easily have provided an unfair and lucrative advantage in the financial markets, either by Epstein himself or by his associates,” Cooper said in the letter, seen by the Guardian. “Mandelson could also have personally profited from this arrangement.”

She added: “He and others must face criminal prosecution if they are found to have abused trading laws for financial benefit.”

Insider dealing is a serious criminal offence, with the harshest penalty in the UK resulting in 10 years in jail, or up to seven years for offences committed before 1 November 2021.

The letter to the FCA comes after emails in the latest tranche of Epstein files appeared to show that Mandelson, when serving as the business secretary under the then prime minister, Gordon Brown, gave Epstein advance warning of market-moving events. That apparently included information on sensitive fiscal and political developments including Brown’s own resignation, as well as a €500bn eurozone rescue deal.

Those emails appear to have been sent to Epstein hours before they were publicly announced in May 2010. Both those events shifted the price of stocks and currencies, including of the British pound. It came at a febrile moment for global markets and local economies, which were still struggling to stabilise after the 2008 financial crisis.

Cooper, who also serves as the Lib Dems’ Treasury spokesperson, pointed to emails apparently showing that Mandelson forwarded a confidential document to Epstein in June 2009 outlining policy options to shore up the UK’s public finances, including selling off £20bn worth of assets.

She also highlighted the exchange in which Mandelson seems to tell Epstein that the JP Morgan chief executive, Jamie Dimon, should “threaten” the Treasury over its plans to tax bankers’ bonuses in December 2009.

The revelations have sent shock waves through Westminster, and led to Mandelson’s resignation from the Labour party on Sunday. Mandelson, who was sacked as the UK’s ambassador to the US in September 2025, resigned from the House of Lords on Tuesday.

The Metropolitan police have launched a criminal investigation into Mandelson over allegations he leaked market-sensitive emails to Epstein, who died in prison in 2019 while awaiting trial over child sex-trafficking charges.

“No individual, regardless of their standing or former office, should be permitted to compromise the integrity of the UK’s financial system by treating confidential state information as a private commodity,” Cooper’s letter said. “I therefore urge the FCA to launch an immediate investigation into whether Peter Mandelson’s actions constitute a criminal offence under insider trading laws.

“The victims who suffered such awful abuse at the hands of Jeffrey Epstein deserve to know the full scope of the financier and his network’s crimes.”

A spokesperson for the FCA said: “The [Met] police has already announced a criminal investigation. It wouldn’t be appropriate to comment any further.”

Mandelson was approached for comment.