A government spokesman said: “The Government stands ready to provide whatever support and assistance the police need.”
Mandelson stepped down as a member of the House of Lords earlier on Tuesday, two days after he quit the Labour Party to avoid causing “further embarrassment”.
He was reported to the police on Monday over allegations of misconduct in public office, which carries a maximum sentence of life imprisonment.
Prosecutors would have to prove that Mandelson was guilty of “wilful neglect or misconduct”, amounting to an “abuse of the public’s trust” without “reasonable excuse of justification”.
On Tuesday, Brown wrote to Met Commissioner Sir Mark Rowley with information relating to the case.
The Cabinet Office also passed a dossier to police after finding that safeguards had been “compromised”.
A Downing Street spokesman said: “An initial review of the documents released in relation to Jeffrey Epstein by the US Department of Justice ... found that they contain likely market-sensitive information surrounding the 2008 financial crash and official activities thereafter to stabilise the economy.
“Only people operating in an official capacity had access to this information and [there were] strict handling conditions to ensure it was not available to anyone who could potentially benefit from it financially.
“It appears these safeguards were compromised. In light of this information the Cabinet Office has referred this material to the police.”
‘Inexcusable and unpatriotic’
The leaked information, which Epstein could have used to make money, included plans for the potential sale of government land and property.
They also suggest the peer gave Epstein advance notice of an impending bailout from the EU to Greece to shore up the euro. The evening before the announcement in 2010, he told Epstein: “Sources tell me 500 b euro bailout, almost complete”.
The emails also show that Mandelson told Epstein that Brown was going to resign in 2010, hours before an official announcement was made.
On the morning of May 10, he appeared to tell him: “Finally got him to go today”. In the evening, Brown announced he was stepping down as Labour leader.
Brown said in a statement on Tuesday: “I have today written to the Met Commissioner Sir Mark Rowley with information relevant to his investigation of Lord Mandelson’s disclosure of market sensitive and confidential government information to the American financier, Jeffrey Epstein, an inexcusable and unpatriotic act at a time when the whole government and country were attempting to address the global financial crisis that was damaging so many livelihoods.”
It was announced on Tuesday that Mandelson would stand down from the House of Lords.
He resigned under the 2014 House of Lords Reform Act, relinquishing his peerage. However, an Act of Parliament must be passed to strip him of his title.
A Downing Street spokesman said: “It is right that Peter Mandelson will no longer be a member of the House of Lords. As the Prime Minister said this morning, Peter Mandelson let his country down.”
Starmer said he should lose his title for bringing the House of Lords “into disrepute” and his official spokesman opened the door to wide-reaching Lords reform that would make it easier for peers to be stripped of their titles.
The Titles Deprivation Act 1917, which would remove Mandelson’s title, was last used in 1917 against a group of peers who had aided enemies of Britain during the war.
Starmer is now under pressure to bring in legislation that would remove his title altogether.
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