Peter Mandelson has been warned by one of his predecessors of one inevitable problem he will have with the next Trump administration.

The Labour peer and former cabinet minister is expected to take up the role in the New Year, although the government is yet to confirm it.

Unlike the president-elect, he is pro-EU and wants more cooperation with China.

Mandelson also condemned Trump’s approach to trade in 2018, saying he is “a bully and mercantilist who thinks the US will gain in trade only when others are losing”.

However, these were not the main issues former US ambassador Kim Darroch mentioned when speaking to BBC Newsnight on Thursday.

He said there was another problem looming for the Labour grandee: Trump’s 5am posts on the social media platform, X (formerly Twitter).

Speaking to BBC Newsnight, the cross-bench peer said: “One thing that is a certainty for the Trump government is the 5am tweet storm that comes most mornings of the week.

“At some point, Trump will say something that will be quite a story in the UK, he did so several times in his first term.

“So Peter Mandelson, I’m sure, will be prepared for that and be prepared for a bumpy and difficult ride.

“But he clearly wanted the job very much, so I say good luck to him.”

Darroch was the US ambassador between 2016 and 2019, but left the role after memos in which he described the first Trump administration as “dysfunctional, inept and divided” were leaked.

Despite concerns that the new UK representative could clash with Trump when it comes to trade, Darroch said he thought Mandelson would be “very well-placed” to explain to the incoming president why 20% tariffs are a “a really bad idea.”

The former US ambassador also claimed Mandelson will be able to repair the current government’s image across the pond.

He said: “There is something of an issue about the government’s reputation with the Trump crowd.

“Look at that accusation before the election that this was a far-left government, look at Elon Musk, saying that the UK has become a tyrannical police state.

“I think Peter Mandelson is exactly the man to persuade them that this is completely wrong, because it is.”

Trump wanted Nigel Farage, now an MP and leader to Reform, to replace Darroch during his first term in the White House.

The far-right politician also told the BBC last month that Trump would “love it” if he were to take up the role for the Republican’s second term, although he acknowledged: “It is not going to happen.”

But Mandelson said in November month that the government should consider using Farage as a “bridge” to Trump and his new right-hand man Elon Musk.