Donald Trump should not block people from his Twitter account just because he doesn’t like their views, a US court has ruled.

The federal appeal court said the president’s use of Twitter’s blocking function was a violation of the US Constitution’s First Amendment.

The decision comes as Mr Trump, who has 61.8 million Twitter followers, ramped up his Twitter rage against Britain after leaked memos written by the UK’s ambassador described Mr Trump as “dysfunctional” and “inept”.

Mr Trump lashed out further at “foolish” British Prime Minister Theresa May and her “wacky” Washington ambassador Kim Darroch.

The British have not condemned their ambassador’s frank assessment of Mr Trump’s administration.

“The wacky Ambassador that the UK foisted upon the United States is not someone we are thrilled with, a very stupid guy,” Mr Trump tweeted, describing Mr Darroch as a “pompous fool”.

“He should speak to his country, and Prime Minister May, about their failed Brexit negotiation, and not be upset with my criticism of how badly it was handled. I told (at)theresa_may how to do that deal, but she went her own foolish way – was unable to get it done. A disaster!”

The wacky Ambassador that the U.K. foisted upon the United States is not someone we are thrilled with, a very stupid guy. He should speak to his country, and Prime Minister May, about their failed Brexit negotiation, and not be upset with my criticism of how badly it was…

— Donald J. Trump (@realDonaldTrump) July 9, 2019

Ms May’s potential replacement as prime minister, Jeremy Hunt, fired back his own Twitter retort, challenging the president’s “disrespectful and wrong” comments and backing the UK’s ambassador.

“You said the UK/US alliance was the greatest in history and I agree,” Mr Hunt said on Twitter.

“But allies need to treat each other with respect as (at)theresa_may has always done with you. Ambassadors are appointed by the UK government and if I become PM our Ambassador stays.”

1/2 @realDonaldTrump friends speak frankly so I will: these comments are disrespectful and wrong to our Prime Minister and my country. Your diplomats give their private opinions to @SecPompeo and so do ours! You said the UK/US alliance was the greatest in history and I agree… https://t.co/hNeBWmyyVN

— Jeremy Hunt (@Jeremy_Hunt) July 9, 2019

Mr Trump has made his (at)RealDonaldTrump account a central and controversial part of his presidency, using it to promote his agenda and to attack critics.

His use of the Twitter blocking function was challenged by the Knight First Amendment Institute at Columbia University, as well as seven Twitter users he had blocked.

“The decision will help ensure the integrity and vitality of digital spaces that are increasingly important to our democracy,” Jameel Jaffer, the Knight institute’s executive director, said in a statement.

In a 3-0 decision, the 2nd US Circuit Court of Appeals in Manhattan said the First Amendment forbids Mr Trump from limiting access to his account.

“The First Amendment does not permit a public official who utilises a social media account for all manner of official purposes to exclude persons from an otherwise open online dialogue because they expressed views with which the official disagrees,” Circuit Judge Barrington Parker wrote, citing several Supreme Court decisions.

Mr Parker said the president’s account bears “all the trappings of an official, state-run account” and is “one of the White House’s main vehicles for conducting official business”.

He said Mr Trump and his aides have characterised the president’s tweets as official statements and the National Archives viewed the tweets as official records.

Mr Parker also found it ironic that Mr Trump censored speech at a time when the conduct of the US government and its officials was subject to intense, passionate and wide-open debate.

“This debate, as uncomfortable and as unpleasant as it frequently may be, is nonetheless a good thing,” he wrote.

“We remind the litigants and the public that if the First Amendment means anything, it means that the best response to disfavoured speech on matters of public concern is more speech, not less.”

Neither the White House nor the US Department of Justice immediately responded to requests for comment.

The decision upheld a May 2018 ruling by US District Judge Naomi Reice Buchwald in Manhattan, which prompted Mr Trump to unblock some accounts.

-with AAP