Mr Trump presided over an extraordinary pre-inauguration rally last night where he danced with the Village People to YMCA

Mr Trump seemed to be enjoying himself at the bash in Washington

Elon Musk, one of Mr Trump’s biggest backers, brought his son X up on to the stage

Some forecasters believe the commander-in-chief’s vow to impose ‘beautiful’ tariffs policies will leave the UK economy 0.9 per cent smaller than it would have been by 2029. House of Commons Library estimates suggest that could mean defence spending being £2billion lower.

Mr Trump spent the eve of the inauguration at a rally, where he declared his supporters had ‘built a new American majority that will lead our country to success for generations to come’.

UK politicians including Nigel Farage, Liz Truss and Suella Braverman are in Washington DC ahead of the ceremonies.

Asked whether previous jibes about Mr Trump by current ministers could be the reason for the lack of invites, the PM’s official spokesman said: ‘No, and look, as I say, the UK and US have a deep and special relationship across wide range of important areas.’

Challenged whether Ms Meloni’s attendance was a cause for concern, the spokesman said: ‘No, and you know, ultimately, the UK and US have got a unique relationship when it comes to a wide range of issues.

‘And the Prime Minister and president Trump have already had many conversations about, you know, where we can deepen that relationship, and we look forward to continuing to work together in the years to come.’

Along with appealing for an early invite to the White House for Sir Keir, a second state visit to Britain for Mr Trump could be on the cards.

But other potential flashpoints include Labour’s plan to hand the Chagos Islands to Mauritius, and whether he maintains support for Ukraine in the war against Russia.

The Mail on Sunday revealed yesterday that some of Mr Trump’s key advisers are debating whether to put Sir Keir ‘at the back of the queue’ of world leaders invited to Washington.

One Trump ally warned the PM was ‘gonna have to eat humble pie’ to get a speedy visit to the White House.

Mr Trump’s campaign filed a Federal Election Commission complaint against Labour in October, accusing it of ‘blatant foreign interference’ after the party’s head of operations, Sofia Patel, asked for people to travel to the US to campaign for Harris.

In an interview with the BBC, Mr Lammy said: ‘I think that when you look at past prime ministers, it’s taken between a week or up to a month to come to Washington. The importance is the strength of the relationship and the serious discussions that we have.

‘In the end, we have war in Europe, we have a ceasefire in the Middle East, but it’s incredibly fragile, and there are important malign actors like Iran that we’ve got to discuss with the United States and, of course, our growing trade relations with the United States.

‘So, lots to discuss, and I’m very confident that Keir Starmer will be discussing this with Donald Trump within the next few weeks.’

Mr Lammy insisted New Labour architect Lord Mandelson is the ‘right man for this moment’ with experience as a former business secretary and EU trade chief.

‘He’s looking forward to presenting his credentials to Donald Trump,’ Mr Lammy said.

Mr Lammy also said he was confident that the intelligence and military agencies in the US would persuade the new president that the Chagos deal is good for all sides.

Nigel Farage (right) was at the rally along with MMA fighter Conor McGregor (left)

Former Pm Liz Truss is also in Washington DC, pictured attending a party for TikTok influencers last night

The UK plans to cede sovereignty of the British Indian Ocean Territory to Mauritius, leasing back the strategically important Diego Garcia base used by the US for 99 years at a reported annual cost of around £90million.

But Mr Trump’s former national security chief HR McMaster told the BBC: ‘I think surrendering the Chagos Islands, or putting the Chagos Islands in a situation where they can easily be coerced, by the Chinese Communist Party for example, I hope it’s a position that we see reversed here by Donald Trump, and by the UK government.’

In his message, Sir Keir dropped a heavy hint that he wants to pursue a Transatlantic trade deal, something that was being intensely negotiated during the last Trump administration.

‘For centuries, the relationship between our two nations has been one of collaboration, cooperation and enduring partnership. It is a uniquely close bond,’ Sir Keir said.

‘Together, we have defended the world from tyranny and worked towards our mutual security and prosperity.’

The Prime Minister and the president-elect met in New York in September at Trump Tower, ahead of the US election, and at the time Sir Keir said he is a ‘great believer in personal relations on the international stage’.

Mr Trump spent the eve of the inauguration at a rally, where he declared his supporters had ‘built a new American majority that will lead our country to success for generations to come’

Sir Keir added: ‘Since our first meeting in September, the President and I have spoken about the need to deepen and invest in the transatlantic relationship.

‘We will continue to build upon the unshakeable foundations of our historic alliance as we tackle together the global challenges we face and take our partnership to the next level focused on shared opportunities ahead for growth.

‘I look forward to our next meeting as we continue our shared mission to ensure the peace, prosperity and security of our two great nations.

‘The special relationship between the United Kingdom and United States will continue to flourish for years to come.’