“They’re not Siamese twins, President Trump and Prime Minister Starmer, but they’re both pragmatic people. They know where each is coming from, they want to find common ground,” Mandelson said. “I feel very optimistic. I feel very upbeat about the relationship that they’re both going to have.”

Mandelson is the first non-career diplomat to take up the job as chief U.K.-U.S. liaison in over half a century. That could prove beneficial for Mandelson when up against Trump, who has long strayed from engaging in traditional diplomacy.

“The president isn’t a career diplomat, and I’m not a career diplomat,” Mandelson said. “I came into politics to change things for the better for people, and so did he.

“We share a similar, if not identical, outlook on the world and motivation in politics. But I think above all, we believe in something which is really special between our countries,” he added, pointing to the enduring relationship between the U.S. and U.K.

Mandelson said his chief priorities will be to work with the U.S. on trade, technological developments and defense partnerships – particularly in the face of adversarial powers like China.

“I think that the United States and Britain, working together, can outsmart and keep ahead of the curve as far as China is concerned,” the incoming ambassador said. “[Trump] wants a dialogue with China, he wants to do deals with China. But he’s also not going to be naive about China. 

Britain’s Prime Minister Keir Starmer addresses members at the Labour Party in Liverpool, England, on Tuesday. (AP)

“We face a challenge together from China, and we’ve got to make sure that we are able to deter that challenge or that threat when they’re having aggressive intents toward us,” he added. 

Mandelson championed the trilateral alliance shared by the U.S., the U.K. and Australia, established with the intent of countering China’s aggression in the Indo-Pacific. 

“Security in the Euro-Atlantic area depends on making sure that China is kept at bay in its own region,” he said. “China has the right to prosper, to generate higher standards of living for its own people, but not at the expense of others.”

Mandelson argued that despite international apprehensions over certain security uncertainties under the Trump administration, the U.K. does not share in these concerns.

“There are so many threats and challenges the world is facing at the moment. It takes courage, somebody, sometimes, who’s prepared to be argumentative and, indeed, disruptive, not just take business as usual,” he detailed.

“Frankly, I think President Trump could become one of the most consequential American presidents I have known in my adult life,” Mandelson said.