When Labour lost the 2010 election, rising star Ed Miliband was asked whether Peter Mandelson, who had just published a headline-grabbing autobiography, could play a role in the party’s future.

“All of us,” Miliband drily replied, “believe in dignity in retirement.”

Mandelson winced and smiled at that quip, he later wrote. But ignored the advice.

Fifteen years later, at the age of 71, the political veteran who helped mastermind Labour’s renewal in the 1980s and 1990s, and was twice forced to resign from Tony Blair’s government, has staged yet another comeback.

“It’s a whirlwind,” admits a member of his new team in Washington. “Because he’s a whirlwind kind of guy.”

The first political appointee to the role of UK ambassador to the United States in 50 years arrived in DC with a lot on his plate. Even by American standards.

But why did Sir Keir Starmer recruit him, what explains Mandelson’s hunger for the job, and how does he plan to charm Team Trump?

“Peter is supremely political,” explains a Downing Street source. “And this is a very political White House. He is a brilliant operator.”

Lord Mandelson has already moved into the ambassador’s vast official residence, recently refurbished at a cost of £118.8m.

His new life will involve more than Congressional meetings and cocktail parties. He now oversees 800 UK staff in the country many of whom are seconded to the Pentagon and defence bases.

At the embassy, beneath a Warhol portrait of the late Queen, Mandelson has already hosted lunch for General Keith Kellogg, President Trump’s envoy to Ukraine and Russia.

This was merely a warm up for the real challenge later this month: accompanying Keir Starmer to the Oval Office to meet President Trump.

The new president may be erratic and impulsive yet No 10 officials are determined the two leaders will develop a strong relationship despite their differing personalities.

“The PM will be asking Peter: ‘How on earth do I handle this crazy guy?’,” says a former colleague.

“As an ambassador in the court of Donald Trump you need someone who can tickle him under his chin. Peter will be the absolute fixer and bridge builder.”

Unlike the imminent turnover of leaders in continental Europe (Mandelson’s long friendship with Emmanuel Macron is no longer so helpful), Starmer and Trump are likely to be in office and working together for the next four years.

One official says part of the UK’s pitch is about emphasising that both men are winners: “Our message to him is we won big in July. You won big in November. Let’s do business together.”

Mandelson has regularly provided advice to Keir Starmer in recent years and acted as an unofficial mentor to the PM’s chief of staff Morgan McSweeney and director of communications Matthew Doyle.

These relationships suggest Downing Street and the US embassy will have an unusually close and constant level of contact.

In an administration where billionaire businessmen have unprecedented influence, Peter Mandelson’s contacts from his time as EU trade commissioner, UK business secretary, and via his international lobbying firm Global Counsel is already being deployed. “He’s essentially been a businessman for the last 15 years,” says a source.

In conversations with Trump, Mandelson could drop the names of numerous mutual friends: he knows Peter Thiel, the right-wing billionaire backer of vice president JD Vance, and Marc Andreessen, co-founder of Netscape, who is on the board of Meta.

Mandelson has met Elon Musk, holidayed with Trump’s new Treasury Secretary Scott Bessent, and built a relationship with Mark Burnett, the TV producer behind The Apprentice who is now Trump’s special envoy to the UK.

Yet Mandelson’s expertise in charming these elites (former President George W. Bush nicknamed him ‘Silvertongue’), and his penchant for luxury have also led to problems throughout his career.

“He has weaknesses,” says one longtime friend. “He likes the high life. A lifestyle he can’t afford.”

Peter Mandelson’s friendship with Russian oligarch Oleg Deripaska during his time at the EU provoked questions about conflicts of interest – Mandelson had stayed on Deripaska’s yacht. The European Commission cleared him of wrongdoing.

A name Mandelson will likely not drop in Trump’s company is that of their late former friend Jeffrey Epstein.

Both knew the billionaire paedophile who died by suicide in 2019. Mandelson maintained a relationship with him even after Epstein signed a plea deal in 2008 and served an 18-month jail term for soliciting sex from girls as young as 14.

Epstein is said to have referred to Mandelson as “Petie”. Photographs released in court documents show Mandelson trying on a belt alongside Epstein in a clothing shop, and the pair blowing out candles on a birthday cake.

Lord Mandelson has said he “deeply regrets” both ever meeting Epstein and the hurt caused to his many victims, and has also said that he never had any kind of professional or business relationship with him. But in an interview with the Financial Times this week, the diplomat also added: “I’m not going to go into this”, and swore explosively at the interviewer.

That undiplomatic language was a rare media misstep and contrasts with No 10’s expectation that Mandelson will be a far safer pair of hands with journalists than his predecessor, outgoing ambassador Dame Karen Pierce.

“Karen just wasn’t reliable enough for broadcast,” one senior insider tells me. Starmer aides want Mandelson to regularly appear on US TV, including Trump’s favoured channel Fox News.

Dame Karen’s glittering career as a diplomat may have meant she had less experience of television, but her expertise in national security and persistence in charming Trump’s allies paid dividends.

So much so that Donald Trump’s co-campaign manager Chris LaCivita objected to Sir Keir replacing a “professional universally respected ambo [ambassador] with an absolute moron”.

Dame Karen stood out in the largely male and often stale world of Washington in her colourful tailor-made suits, occasionally complemented with a feather boa.

As she packed her bags, at one farewell event she was presented with a commemorative champagne sabre engraved with the words “always the Dame of DC”.

Swapping a beltway bon vivant for the so-called Prince of Darkness is, however, a risk.

Concerns have been raised about potential conflicts with clients of Mandelson’s lobbying firm Global Counsel, which have included Shell and China-linked companies like TikTok. He resigned from Global Counsel’s board last summer but remains a shareholder.

Mandelson has already appeared on Fox News to apologise for his previous criticism of Donald Trump. He said his claims that the president was “a bully” were “ill-judged and wrong”.

Friends say the new ambassador is well aware that even before he arrived in the US capital he had other prominent detractors like Steve Bannon, Trump’s former top adviser who called his appointment a “terrible pick”.

Mandelson’s diplomatic strategy so far involves dividing Trumpworld into three groups and approaching them in different ways. The groups are: ideological MAGA (Trump’s campaign mantra Make America Great Again), national security MAGA, and the technocracy.

The first of these groups includes Bannon and may be the trickiest to mollify.

“They want to do as much damage as possible to Starmer and the UK/US relationship,” says a diplomat. “And they want to discredit Peter.”

Mandelson privately considers himself a foreign policy hawk so is more optimistic about his luck with group two: national security MAGA. These officials are more anti-Putin than others in the president’s orbit, and they could be helpful when discussing policy on Ukraine, Russia and China.

Group three – the technocracy – should also be open to the ambassador’s advances. Mandelson wants the signature policy of his time in Washington to be a technological partnership involving AI and quantum computing.

“So Western nations and economies retain a technological edge over our adversaries,” explains one involved.

Before all that, the most pressing priority for the UK is avoiding trade tariffs.

To help smooth the path, Mandelson’s team have pointedly decided to frame their interactions with the White House in America First terms.

“We have a balanced trading relationship with America,” insists one British diplomat.

“We’ll be demonstrating where the UK partnership adds value to America not just saying ‘this is good for Britain’.”

As the president floats unconventional and controversial ideas, one key UK tactic will be to simply stay out of the President’s firing line.

“We’re not getting involved,” is a regular refrain from Downing Street.

On Monday, Lord Mandelson will present his diplomatic credentials (a formal letter from King Charles) at the State Department.

He is understood to already be planning how best to deploy his ultimate line manager with officials considering inviting the president on a second state visit to London.

President Trump appeared to revel in a recent meeting with Prince William, who he said “looks better in person”.

Trump also insists, without evidence, he was Elizabeth II’s favourite president.

One minister jokes that when the prime minister visits the White House later this month he should take “something from the Buckingham Palace gift shop… Maybe give Trump a royal family colouring-in book”.

Forty years after he became Labour’s director of research and communications, Peter Mandelson is back at the heart of British politics.

As to why he still has the hunger for high office, one friend points to the four years he spent in the political wilderness after resigning from Tony Blair’s government for the second time in 2001.

That bruising experience, they argue, left him feeling unfulfilled and desperate to prove himself.

“He should have been foreign secretary,” says the friend. “Instead in those years he sat at home watching his contemporaries and intellectual inferiors on Newsnight.”

Another ally characterises Lord Mandelson’s ambition in simpler terms: he has an insatiable thirst for power.

“Peter’s great mission in life”, they say, “is to stay relevant.”