Peter Mandelson’s position as the frontrunner to be British ambassador to the US has been questioned after it emerged he criticised Donald Trump for being a “bully” and too hostile towards China on trade policy.

Critics of Beijing raised concerns over the suitability of the Labour peer to take on the job given his repeated defence of engagement with China, while Trump’s administration is hawkish towards the rival trading power.

Mandelson is understood to be in pole position for the Washington job, on a shortlist with David Miliband and Cathy Ashton, and has been even-handed when talking about Trump in recent months.

But in 2018, he wrote an article arguing Trump’s hostility towards China was putting free trade at risk, while describing him as a “bully and mercantilist”.

“It is absurd to imagine putting a country of such weight in the naughty corner,” he said of US relations with China in 2018.

“It is also necessary to recognise Mr Trump’s behaviour for what it is: he is a bully and a mercantilist who thinks the US will gain in trade only when others are losing.

“His idea of a progressive trade policy is one that forces everyone else to give the US more favourable treatment rather than a trading system from which everyone gains.”

Mandelson has spoken up in favour of thawing relations with China, which soured under successive Conservative leaders over security and hacking concerns. In September, he criticised the previous Tory government for being in danger of operating a “boycott of Hong Kong and the necessary communication that Britain needs to maintain with China”.

Global Counsel, the advisory firm cofounded by Mandelson, counted a Chinese state-owned company as a client in 2014 but it has not worked for government-backed entities since then. The Guardian reported on Tuesday that Global Counsel advised the Chinese fast fashion company Shein until earlier this year.

Mandelson, 71, stepped down from Global Counsel’s board in June but remains its president and retains a substantial stake.

According to its declaration to the lobbyists registrar, Global Counsel’s clients include TikTok, which is owned by the Chinese technology company ByteDance and was banned from UK government devices last year.

Iain Duncan Smith, a Conservative MP and former party leader, who faced sanctions from China in 2021, said: “For this new Labour government, it is important to have an ambassador that is able to get close to the new Trump administration and be trusted by them.

“It is hard to see that someone … who has such strong connections to China at a time when the US sees China as a threat will be welcome in Washington.

“Whilst I am a Conservative, I recognise the need for the UK to be very close to the USA. We should have learned our lesson over the previous problems with Kim Darroch. If Mandelson is the answer, what then was the question?”

David Alton, a Liberal Democrat peer and critic of China, said: “Unnecessarily putting the UK at odds with the US over China policy would not be in our national interest or in the interests of those suffering at the hands of the Chinese Communist party (CCP) – from Uyghur Muslims subject to genocide, to pro-democracy advocates imprisoned in Hong Kong, or the 23 million Taiwanese facing daily military intimidation.

“We need to speak with one voice and not send contradictory and confusing messages. The choice of UK ambassador to the US will speak volumes about how we intend to respond to the global threat posed by the CCP [Chinese Communist party] and to the largely bipartisan China policy of the USA.”

Luke de Pulford of the Inter-Parliamentary Alliance on China, a group critical of Beijing, said Mandelson would be the “worst possible appointment” for US ambassador, and would “go down like a cup of cold sick in the US”.

However, Mandelson has won unexpected support for the role from the Reform UK leader Nigel Farage, an ally of Trump. He said earlier this week: “Peter Mandelson, in my view, could be a viable candidate for the ambassadorial role.

“He’s an intelligent figure who knows his brief well, as I saw when he worked with the European Commission.

“While I’m not certain he’s the ideal fit for dealing with Trump directly, his intellect would at least command respect.”

Mandelson was approached for comment.