President Trump on Tuesday, in a press conference with outgoing U.K. Prime Minister Theresa May, blasted his British left-wing critics as a "negative force" -- and confirmed that he snubbed the leader of the opposition Labour Party when he sought a sit-down.

"I don't know Jeremy Corbyn, never met him, never spoke to him -- he wanted to meet today or tomorrow and I decided I would not do that," Trump told reporters at the London press conference.

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"I think that he is, from where I come from, somewhat of a negative force. I think people should look to do things correctly as opposed to criticize. I really don't like critics as much as I like and respect people who get things done," he said.

Corbyn, the Labour Party leader and a veteran left-wing activist, was attending an anti-Trump protest as the press conference was ongoing. During that, he said he was "not, absolutely not, refusing to meet anybody."

"I want to be able to have that dialogue to bring about the better and more peaceful world we all want to live in," he said.

Trump also took another shot at longtime foe and London Mayor Sadiq Khan, who had also opposed Trump's visit to Britain.

"I don't think he should be criticizing a representative of the United States that can do so much good for the United Kingdom," Trump said. "He's a negative force, not a positive force."

Of the mayor, Trump said: "He's done a poor job, crime is up, a lot of problems."

May was similarly critical of the left-wing detractors. While noting differences with the Americans on issues such as Iran and the Paris climate deal, she highlighted the importance of the special relationship between the two countries to British citizens at home and abroad and to the British economy as a whole.

"That is a relationship that we should cherish, it is a relationship we should build on and should be proud of," she said.

"This really is a very big and important alliance and I think people should act positively toward it because it means so much for both countries," Trump agreed.

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The press conference comes amid a three-day state visit for Trump, which has included a meeting with Queen Elizabeth II and a state dinner at Buckingham Palace. He will mark the 75th anniversary of D-Day in Portsmouth, before traveling to France to take part in celebrations there.

But while the visit has included a fair amount of pomp and circumstance, it has not stopped Trump from bringing his own brand of bare-knuckle politics to Blighty -- with him calling Khan a “stone cold loser” on Monday.

“Kahn reminds me very much of our very dumb and incompetent Mayor of NYC, [Bill] de Blasio, who has also done a terrible job -- only half his height,” he said.

His remarks were apparently in response to an op-ed by Khan, in which the mayor called Trump "one of the most egregious examples of a growing global threat."

"That’s why it’s so un-British to be rolling out the red carpet this week for a formal state visit for a president whose divisive behaviour flies in the face of the ideals America was founded upon -- equality, liberty and religious freedom," he wrote.

Trump has also brushed aside diplomatic norms in weighing in on the race to succeed May as prime minister. May will step down from Number 10 on Friday and a leadership contest will begin days later.

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Britain was due to leave the bloc in March, but that has been delayed until Oct. 31 after Parliament rejected three times the withdrawal agreement May thrashed out with European leaders last year. Trump has thrown most of his backing behind former Foreign Secretary Boris Johnson, a hardline Brexiteer born in New York who has warmed to Trump in recent years.

Trump said Tuesday that he's liked Johnson "for a long time" and also said that Foreign Secretary Jeremy Hunt would be a strong candidate.

"I know Boris, I like him, I've liked him for a long time. I think he'd do a very good job I know Jeremy, I think he'd do a very good job," he said.

The Daily Telegraph reported that Johnson turned down a one-on-one meeting with the president because it clashed with a leadership debate, but that the two will speak by phone.

Beyond the race to succeed May, Trump has also given his support to Brexit Party leader Nigel Farage, whom he praised for finishing first in the recent European Parliament elections.

“Nigel’s had a big victory, he picked up 32 percent of the vote starting from nothing, and I think they’re big powers over there -- I think they’ve done a good job,” Trump said last week.

The American president’s visit comes at a critical time for the U.K. Should Brexit go ahead, a U.S.-U.K. trade relationship will be key to Britain’s post-Brexit success. Trump used the press conference to double down on his support for a deal.

“There is tremendous potential in that trade deal, I would probably say two or three times what we are doing now,” he said.

While he has been critical of May's handling of Brexit in the past, on Tuesday he was more diplomatic: "Perhaps you won't be given the credit you deserve...you deserve a lot of credit." But he also joked with May about past advice that he gave her to sue to E.U. instead of negotiating with the European behemoth.

"I would have sued but that's OK. I would have sued and settled maybe, but you never know, she's probably a better negotiator than I am," he said.

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But Trump will also face a significant protest in the capital on Tuesday, where left-wing activists and politicians are due to march in protest of the visit -- similar to a large protest that took place during Trump’s working visit to the country last year.

Trump said he had only seen a "small protest" and said he had instead seen a lot of support from Brits: "It was a very, very small group of people put in for political reasons."