Sir Keir Starmer said the UK-US special relationship will “continue to prosper” following Donald Trump’s “historic election victory”.

Mr Trump declared he had won a “magnificent victory for the American people” once it was clear he was on track to return to the White House as 47th president of the United States.

That victory was later confirmed as a win in Wisconsin tipped him over the 270 electoral votes needed to defeat Kamala Harris.

Sir Keir will be keen to build bridges with Mr Trump after the Republican politician’s campaign filed a legal complaint about Labour activists supporting Ms Harris.

The Prime Minister said: “Congratulations president-elect Trump on your historic election victory. I look forward to working with you in the years ahead.

“As the closest of allies, we stand shoulder to shoulder in defence of our shared values of freedom, democracy and enterprise.

“From growth and security to innovation and tech, I know that the UK-US special relationship will continue to prosper on both sides of the Atlantic for years to come.”

The return of Mr Trump to the White House could cause diplomatic headaches for the UK, with potential splits on trade policy and US support for Ukraine and Nato.

Foreign Secretary David Lammy said he is looking forward to working with Mr Trump and his running mate JD Vance.

Mr Lammy has spent time seeking to form a close relationship with the Trump campaign, despite a history of outspoken criticism of his record – including calling him a “racist and KKK/neo-Nazi sympathiser” in 2017 and a “tyrant in a toupee” a year later.

“The UK has no greater friend than the US, with the special relationship being cherished on both sides of the Atlantic for more than 80 years,” Mr Lammy said on Wednesday.

With projections showing Mr Trump was on course for a spectacular return to the White House, the Republican candidate told his supporters that “America has given us an unprecedented and powerful mandate”.

He said that he would not let his backers down and that it is “time to put the divisions of the past four years behind us”, as he looks likely to win the presidency for the second time.

Addressing a campaign party in Florida in the early hours of Wednesday, Mr Trump pledged to “fight” for “every citizen” and promised the “golden age of America”.

He said: “Every single day I will be fighting for you with every breath in my body.

“I will not rest until we have delivered the strong, safe and prosperous America that our children deserve and that you deserve.”

He added: “This is a magnificent victory for the American people that will allow us to make America great again.”

Mr Trump’s power at the start of his second presidency could be untrammelled, with the Republicans also appearing on course to win a Senate majority and retaining control in the House of Representatives.

The president-elect has long complained about US tax dollars funding European security and has been highly critical about Nato members not spending enough.

He has also repeatedly claimed he would bring the war in Ukraine to an end, although he has not set out how he would achieve this.

Ukraine’s Volodymyr Zelensky was quick to congratulate Mr Trump and said: “I appreciate President Trump’s commitment to the ‘peace through strength’ approach in global affairs. This is exactly the principle that can practically bring just peace in Ukraine closer. I am hopeful that we will put it into action together.

“We rely on continued strong bipartisan support for Ukraine in the United States.”

Nato secretary general Mark Rutte said Mr Trump’s leadership “will again be key to keeping our alliance strong”, adding: “Through Nato, the US has 31 friends and allies who help to advance US interests, multiply American power and keep Americans safe.”

Addressing Mr Trump’s concerns about burden-sharing, he added: “Two-thirds of Allies now spend at least 2% of their GDP (gross domestic product) on defence, and defence spending and production are on an onward trajectory across the alliance.”

Former defence secretary Sir Ben Wallace said the return of Mr Trump should spur European Nato members to commit more to security, with a pledge to spend 3% of GDP.

“Whatever your feelings about the US election are, the best insurance for all our security is to invest in our own defence and security right across Europe,” he said.

Reform UK’s Nigel Farage, a leading supporter of Mr Trump, said the president-elect would be a “genuine radical”.

He told BBC Radio 4’s Today: “What you are going to see from this Trump administration, and I’m guessing that Elon Musk will be the man that is tasked to do it, is there will be a big fightback against the administrative bureaucratic state which is far too big, far too powerful and actually very undemocratic.

“What is very interesting about the Trump movement is that its critics call it all sorts of nasty names, the truth is in many ways it’s bringing Americans together.”