After giving him a third chance in Government and a peerage, Gordon Brown might have expected some gratitude from his erstwhile New Labour enemy.

But in private, Lord Mandelson was not only mocking the then Prime Minister and leaking highly sensitive information he had gleaned from serving as his Business Secretary – but also plotting to take over from him in Downing Street, damning emails suggest.

Files released by the US Department of Justice reveal that Mandelson and financier Jeffrey Epstein were discussing, and often belittling, goings-on in the final days of Mr Brown’s tenure.

As it became clear the writing was on the wall for the Labour leader ahead of the 2010 election, Epstein urged his friend to run for the top job, saying he could be Britain’s answer to Vladimir Putin. 

He said Mandelson could stand on a joint ticket with David Miliband, putting his Cabinet colleague in No 10 as a puppet, as Putin had done in 2008 when he made Dmitry Medvedev president while retaining power.

‘Can we put together for you the equivalent of a Putin Medeyev [sic] deal,’ Epstein said. ‘Choose someone who will be seen to be your stand-in, run as a team. Milibrandelson. The voters would be voting for you?’

It was an interesting comparison from a man some say was heavily linked to Moscow, and maybe even a Russian asset in the US.

The convicted paedophile even discussed an unlikely ploy where Labour’s former spin doctor could enter No 10 by marrying into the Royal Family, so losing his place in the House of Lords.

Peter Mandelson (right) seemingly plotted to oust Gordon Brown as he struggled to cling onto power during his final months in office

Peter Mandelson (left) previously claimed he was ‘kept separate’ from the ‘sexual side’ of paedophile financier Jeffrey Epstein (right)

Mandelson and Epstein appeared to message each other mocking Brown’s inevitable departure just days before he resigned

The pair joked about the peer marrying Princess Beatrice with the paedophile financier describing it as ‘incest’, emails show 

Convention dictates the PM must be directly accountable to the elected representatives of the lower house of Parliament.

In October 2009, Lord Mandelson was told by Epstein: ‘My reading is that if you were to marry Princess Anne, and then divorce you could be prime minister. As the peerage evaporates on a merger with the monarchy. Or you can marry Princess Beatrice, the queen would have a queen as a grandson.’

Lord Mandelson told him ‘Remember, I am already her Lord President.’ To which Epstein replied: ‘Does that make it incest, how exciting.’

Weeks later Epstein suggested: ‘If you married Prince Andrew you would be forced to resign your peerage, and then be prime minister.’ Lord Mandelson replied: ‘It’s a deal.’

In another conversation Lord Mandelson revealed ‘Tony’ had recommended he ‘facilitate not initiate’, and said that Mr Brown would immediately ‘push panic button’ if told to step down.

‘Highly sensitised to movement of my eyebrow,’ he told Epstein of Mr Brown, who had long believed Lord Mandelson had betrayed him by backing Tony Blair to lead Labour.

Epstein seemed obsessed by the idea of Lord Mandelson taking over from Mr Brown, who had dramatically brought him back to Government in 2008, even discussing it with an aide to Microsoft billionaire Bill Gates.

He told Boris Nikolic in January 2010: ‘Unfortunately, he is LORD Mandelson no lord is allowed to be a prime minister.’