Keir Starmer has “utterly rejected” the idea that the UK must choose between the United States and Europe when Donald Trump comes to power, arguing that it is in the national interest to work with both.

The prime minister said the UK would “never turn away” from its relationship with the US, despite the difficulties the new administration could pose, as it had been the “cornerstone” of security and prosperity for over a century.

Yet he would also continue to “reset” Britain’s relationship with Europe, the country’s biggest trading partner, he said, after years of neglect post-Brexit, as strong bilateral links were vital for growth and security.

“Against the backdrop of these dangerous times, the idea that we must choose between our allies, that somehow we’re with either America or Europe, is plain wrong,” he said.

“I reject it utterly. [Clement] Attlee did not choose between allies. [Winston] Churchill did not choose. The national interest demands that we work with both.”

His remarks come after foreign policy and trade experts warned that Trump could pressure the UK to effectively pick sides between it and the European Union if he presses ahead with threatened trade tariffs when he takes over next year.

But despite Labour’s previously tense relationship with Trump, Downing Street sources said they felt equipped to deal with the “unpredictability and noise” that has already started coming their way from Washington.

Starmer’s team, they continued, has spent years preparing for the possibility of a Republican victory – building relationships and, crucially, bridges. However, as some of Elon Musk’s criticism of the prime minister has shown, the usual rules of diplomacy no longer apply.

Instead, the government believes it can capitalise on the global uncertainty that Trump’s presidency creates, with the new administration likely to reverse the US position in conflict zones and embark on a more protectionist approach on trade.

In a major foreign policy speech at the Lord Mayor’s banquet in London, Starmer insisted the UK could be a “constant and responsible actor in turbulent times”, with the return of Trump expected to shake up the global order, including in Ukraine and the Middle East.

“I recall Philip Larkin’s words about her late majesty Queen Elizabeth as a ‘constant good’ – a strong, still point in a changing world – because I think it also reflects Britain and the nation’s role today,” he said.

“To be a constant and responsible actor in turbulent times. To be the soundest ally and to be determined – always – in everything we do.”

In his speech, the prime minister said he would “never turn away” from the UK’s special relationship with the US, even though many inside government privately believe it will prove a difficult path to navigate in coming years.

“This is not about sentimentality,” he said. “It is about hard-headed realism. Time and again the best hope for the world and the surest way to serve our mutual national interest has come from our two nations working together. It still does.”

Starmer has also vowed to turn the page on the UK’s relationship with European partners, putting the fractious relations of the Brexit years behind it. Since taking office he has visited the German chancellor, Olaf Scholz, in Berlin and met the French president, Emmanuel Macron, in Paris. He also hosted 50 leaders from across the continent for the European Political Community meeting within days of taking office.

He told his audience that the government had already improved relations with Britain’s European neighbours, with a “shared ambition to work more closely where necessary”, including through a new security pact covering foreign affairs and defence.

“This is about looking forward, not back,” Starmer added. “There will be no return to freedom of movement, no return to the customs union and no return to the single market. Instead we will find practical, agile ways to cooperate which serve the national interest.”

Ministers are hiring a new EU negotiator to act as a representative for all of the UK’s dealings with the bloc ahead of renewal talks on the trade and cooperation agreement, which underpins the post-Brexit relationship, in 2025.

The government has said that security is the bedrock on which the UK economy rests. “There is no greater responsibility for this government,” the prime minister said. He does not, however, plan to set out a timetable to reach 2.5% of GDP on defence spending until next year.

After becoming the first British leader in six years to meet Xi Jinping, the Chinese president, last month, Starmer argued that the UK could not “look the other way” on China, and instead planned to “keep talking” to Beijing.

Trump is proposing to slap huge 60% import tariffs on China. Trade experts expect that the US will call on the EU and UK to follow suit – a demand that both will strongly resist for their own trade reasons.

The UK is seeking to increase trade with Beijing while also stepping up efforts to find greater ways to access the EU single market.