Nigel Farage has accused Downing Street of putting its dislike for him ahead of the national interest, after aides to the Prime Minister dismissed out of hand a call from Donald Trump for him to be made the UK's ambassador to the United States.

The interim Ukip leader said it was time for Number 10 to recognise that "the world has changed", as he claimed he was "in a good position, with the President-elect's support, to help".

Mr Trump shocked Westminster with a late-night tweet declaring that Mr Farage would do a "great job" and that "many people" wanted to see him as the UK's senior diplomat in Washington.

The property tycoon's highly unusual endorsement was a fresh embarrassment for Theresa May, who was beaten to meeting the future president in person by Mr Farage.

Downing Street immediately retorted that there was "no vacancy" and praised Britain's incumbent ambassador, Sir Kim Darroch.

A No 10 spokesman said: "There is no vacancy. We already have an excellent ambassador to the US."

Mr Farage told the Press Association he was "very flattered" by Mr Trump's suggestion and was ready "to do anything I can to act in a positive way to help relationships between our two countries".

Writing later for website Breitbart - whose former executive chairman Stephen Bannon has been appointed Mr Trump's chief strategist - Mr Farage denounced what he described as "career politicians" who were pretending to be Mr Trump's friend after previously criticising him.

"The political revolution of 2016 now sees a new order in charge of Washington. In the United Kingdom the people have spoken but the players at the top have, I am afraid, stayed the same," he said.

"Those who supported Remain now hold senior positions. Worst still, those who were openly abusive about Trump now pretend to be his friend. It is career politics at its worst and it is now getting in the way of the national interest.

"I have said since the now famous photograph with Donald Trump 10 days ago that I would do anything to help our national interest and to help cement ties with the incoming Anglophile administration.

"At every stage I am greeted by negative comments coming out of Downing Street. The dislike of me, Ukip and the referendum result is more important to them than what could be good for our country.

"I have known several of the Trump team for years and I am in a good position with the President-elect's support to help. The world has changed and its time that Downing Street did too."

Mr Farage's comments may be seen as a reference to Mrs May's previous description of Mr Trump's remarks about Muslims as "divisive, stupid and wrong" at a time when he was seeking nomination as the Republican candidate for president.

Since his election, Mrs May has been careful to avoid any criticism of the president-elect, and Downing Street revealed on Monday that an invitation for a state visit to the UK is under consideration.

Mr Farage described Mr Trump's suggestion that he could be ambassador as "a bolt from the blue", adding that it reflected the fact that the president-elect was "a very loyal man and supports those that stand by him".

"It is called trust and it is how the whole world of business operates," said the Ukip leader.

"Sadly, the cesspit that is career politics understands nothing of this. In their world the concept of trust is transitory."

Mr Farage joined the Republican candidate on the campaign trail, and Mr Trump later described his eventual victory as "Brexit plus plus plus".

The Ukip leader's meeting with Mr Trump in New York came at a time when Mrs May had had only a phone call with the president-elect, and prompted suggestions that Mr Farage could perform a go-between role with the new US administration.

Number 10 rejected at the time suggestions that Mr Farage could be the "third person" in the relationship between the Prime Minister and her US counterpart and insisted that the Government had "well-established" channels of communication.

In the immediate wake of Mr Trump's election, a leaked memo reportedly sent by Sir Kim sought to reassure the Government that UK diplomats were "well placed" to capitalise on change at the White House.

However Mr Farage said it was "obvious" that the ambassador, who took over in January, should resign as he was part of the "old regime".

Mr Trump's suggestion prompted violently contrasting reactions in the UK.

Liberal Democrat leader Tim Farron suggested that the president-elect may be trying to deflect attention from his decision to tear up the TPP free trade deal with Pacific Rim countries, which was signed in February but has not yet been ratified.

"Farage as ambassador is a frankly stupid idea. I have more diplomacy in my little finger," said Mr Farron. "But what's more worrying is the axing of TPP."

TV presenter Gary Lineker described Mr Trump's tweet as "another hilarious joke from the funniest parody account on Twitter," adding: "Nigel the diplomat?....must be Cockney rhyming slang."

But Arron Banks, the millionaire who bankrolled the Leave.eu referendum campaign and joined Mr Farage on his visit to Trump Tower days after the US election, said the Ukip leader would be a good choice as ambassador.

"He would be better than existing one who spent his whole time greasing up to Hillary (Clinton)," said Mr Banks. "The UK would have the best relations with the USA bar none. TM (Theresa May) people insulted Trump."

Asked what he thought of Mr Trump suggesting who the UK should appoint as ambassador, Brexit Secretary David Davis told the BBC: "We are believers in free speech in Britain, but we've got a very good ambassador - Kim Darroch - and he's going to be there for some years.

"People can say what they like. The simple truth is there's no vacancy. This is an ambassador who is very, very good, as we've seen already, and he will be there for years."

Former Ukip MEP Steven Woolfe, who now sits as an independent in the European Parliament, said: "I think Donald Trump has obviously got his own views on how he has a relationship with Britain. He obviously gets on very well with Nigel.

"Whether Nigel would make a good ambassador would be really up to the two governments being able to decide whether he could actually carry out government policy. I don't know - seems we are in a changing world."