Donald Trump has apparently accused the UK of conspiring to help the Obama administration spy on his presidential campaign, saying "when the truth comes out, it will be a beauty!".

The US president promoted the conspiracy theory on Twitter by quoting a right-wing US news organisation's headline, which according to Mr Trump read: "Former CIA analyst Larry Johnson accuses United Kingdom Intelligence of helping Obama Administration Spy on the 2016 Trump Presidential Campaign."

Mr Trump added: "WOW! It is now just a question of time before the truth comes out, and when it does, it will be a beauty!"

GCHQ, the UK government's chief digital spying organisation, branded the allegation "utterly ridiculous".

"As we have previously stated, the allegations that GCHQ was asked to conduct 'wire tapping' against the then President Elect are nonsense. They are utterly ridiculous and should be ignored," the agency told Reuters.

The claim appears to stem from Mr Johnson, a former CIA analyst who is a longtime critic of US intelligence and a defender of Russia.

Mr Johnson has previously claimed without providing evidence the CIA, and not Moscow, may have been behind the hacking of the Democratic National Committee, and has frequently appeared on Russian state media to reject US intelligence conclusions of Russian interference in the 2016 election.

The Guardian reported in 2017 Britain's intelligence agencies had alerted their US counterparts to suspicious "interaction" between figures connected to the Trump campaign and Russian agents, but that it was part of a "routine exchange" of information and that CGHQ never carried out a targeted operation against Mr Trump or his team.

There is no evidence the Obama administration conducted a spying operation against the Trump campaign.

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Mr Trump's tweet followed one last month in which he suggested Britain had invented Russian election interference in order to "bait" the US into taking a hard line against Moscow.

It comes two years after GCHQ was forced to deny it "wire tapped" Trump Tower in 2016, after the White House promoted a Fox News pundit's allegation Barack Obama bypassed US intelligence by using the UK's spy centre to obtain details of Mr Trump's conversations.

"They are utterly ridiculous and should be ignored," GCHQ said at the time.

The president, who has access to information provided by the world's most powerful intelligence agencies, later told reporters "you should be talking to Fox" when asked about the claim.