Britain named Labour Party grandee Peter Mandelson as its ambassador to the United States on Friday, seeking to woo Donald Trump's administration, avoid a trade war, and ensure the countries remain aligned over Ukraine.

A former European commissioner for trade and a key figure in Labour's success under former leaders Tony Blair and Gordon Brown, the 71-year-old is the first political appointee to the role in almost half a century.

His past reputation as a charming but ruthless behind-the-scenes operator saw him dubbed "Prince of Darkness" in U.K. media.

The selection is one of Keir Starmer's most significant foreign policy moves since becoming prime minister in July, given the potential reverberations from Trump's return to power.

Starmer said Mandelson would start early next year, replacing the highly-regarded Karen Pierce: a career diplomat from the politically neutral civil service at the end of her term.

"The United States is one of our most important allies and as we move into a new chapter in our friendship, Peter will bring unrivaled experience to the role and take our partnership from strength to strength," Starmer said in a statement.

Mandelson will have to argue that Ukraine should receive all the support it needs in its war with Russia and that as a close ally, Britain should be spared any trade tariffs Trump may impose.

He may be wary of Trump's well-advertised relationship with Nigel Farage, the populist politician who championed Britain's EU exit and is a vocal critic of Starmer's government.

"We face challenges in Britain but also big opportunities and it will be a privilege to work with the government to land those opportunities, both for our economy and our nation’s security, and to advance our historic alliance with the United States," Mandelson said in a statement.

No stranger to controversy, he was twice forced out of the Cabinet over separate scandals, and his belief in closer ties with China and opposition to Brexit may be at odds with Trump's outlook.

The fate of a previous U.K. ambassador to Washington may serve as a warning. Kim Darroch was forced to quit in Trump's first term when leaked memos showed he had called the U.S. government inept, earning the wrath of Trump, who called him stupid.

Mandelson believes Britain must navigate a path between the U.S. and the EU without choosing one over the other. "We have got to find a way to have our cake and eat it," he told a Times podcast this year.