Donald Trump has used his first official press conference with a foreign leader to throw the full weight of the US Presidency behind Brexit.

Theresa May stood next to President Trump as he declared that a "free and independent" Britain outside the EU would be a "blessing" for the world.

In words likely to antagonise already strained relations with EU leaders, Mr Trump said the UK and US understood that "governments must represent their own citizens" and now Britain would be able to seal trade deals without "somebody watching you".

The Prime Minister made clear her strong desire to build close a relationship with Mr Trump, as she praised his contentious election win as a "stunning victory" and confirmed that he has accepted an invitation for a state visit during which he will meet the Queen.

When May met Trump - five key points from the leaders' press conference

But the big show of togetherness was pricked by the simmering controversies surrounding the Trump administration, including questions over the new leader's approach to torture and Mexico.

Ms May tackled another area of contention – the President’s support for Nato – saying that Mr Trump backed the institution “100 per cent”.

The President has previously called Nato “obsolete” but the Prime Minister said they were in agreement that the organisation is the "bulwark of our collective defence". In return, Ms May said that she would encourage other EU leaders to meet their Nato commitment of spending 2 per cent of national income on defence.

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Mr Trump also renewed his support of torture, but said he would defer to his Defence Secretary, James Mattis, who opposes so-called ‘enhanced interrogation’ techniques.

The press conference was the centre-piece of the Prime Minister's visit, which also saw her woo congressional Republicans at their annual retreat in a bid to strengthen the chances of a future trade deal with the US.

But with the tectonic plates of international politics re-aligning, it was Mr Trump's clear backing for Brexit that gave the clearest indicator of how the President sees a new global order.

Highlighting that he thought the US and UK both valued "prosperity and the rule of law", he said: "That is why the US respects the sovereignty of the British people and their right of self-determination.

"A free and independent Britain is a blessing to the world and our relationship has never been stronger. Both America and Britain understand that governments must be responsible to everyday working people, that governments must represent their own citizens."

Mr Trump has been heavily critical of Germany's Angela Merkel for her decision to allow thousands of immigrants to enter her country and has been accused by EU leaders of fomenting the break up of the union.

Theresa May and Donald Trump were pictured holding hands

During the conference he again talked about the difficulties of doing business in the EU.

He said: "I think Brexit is going to be a wonderful thing for your country. I think when it irons out you're going to have your own identity, and you're going to have the people that you want in your country, and you're going to be able to make free trade deals without having somebody watching you and what you're doing."

The President added: "I think it will go down that it will end up being a fantastic thing for the United Kingdom, in the end it will be a tremendous asset and not a tremendous liability."

He also boasted of having correctly predicted Brexit against the odds while visiting Scotland in June, although he in fact did not hold his press conference there until after the result was already known.

In one awkward moment when British journalist Laura Kuenssberg asked about Mr Trump's questionable views on torture, the President joked about whether Ms May should have asked the BBC Political Editor to speak. “There goes that relationship,” he joked.

But the Prime Minister insisted that she and the President would listen to each other and that she would not be afraid to raise difficult issues.

"There will be times when we disagree and issues on which we disagree. The point of the special relationship is that we are able to have that open and frank discussion so we are able to make that clear when it happens,” she said.

Theresa May congratulates Donald Trump on 'stunning election victory'

"But I am clear also that there are many issues on which the UK and the US stand alongside one another, many issues on which we agree."

At the start of the event Ms May congratulated Mr Trump on what she said was "a stunning election victory", despite him having lost the popular vote.

Amid intense speculation as to how the brash New York property mogul and the vicar's daughter would get along, Mr Trump was spotted taking the Prime Minister by the hand as they walked through the White House grounds.

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Mr Trump insisted that despite their very different backgrounds they were both "people persons". "I am not as brash as you might think,” he said. “I think we are going to get along very well.”

Earlier in the day Mr Trump and the Prime Minister had a brief meeting in the Oval Office, where both were desperate to draw attention to a bust of Winston Churchill that had arrived back in the room.

The pair were also pictured walking hand-in-hand along the colonnade at the back of the White House, with the awkward photos then shared widely on social media.

At lunch the pair and their advisors ate a baby iceberg wedge salad with blue cheese, followed by braised beef shortribs with potato purée and glazed winter vegetables and finished with salted caramel creme brûlée.