A UK spy agency did not eavesdrop on Donald Trump during and after last year's US presidential election, a British security official has said, denying an allegation by a US television analyst.

The official, who is familiar with British government policy and security operations, told Reuters that the charge made on Tuesday by Fox News analyst Andrew Napolitano, was “totally untrue and quite frankly absurd.”

Trump, who became president in January, tweeted earlier this month that his Democratic predecessor, Barack Obama, wiretapped him during the late stages of the 2016 campaign. The Republican president offered no evidence for the allegation, which an Obama spokesman said was “simply false.”

Senior Obama administration officials, including former Director of National Intelligence James Clapper, have also denied any such wiretapping occurred.

On Monday, the US Justice Department told the House of Representatives Intelligence Committee that it needed more time to respond to a demand for copies of any documents that might show Obama ordered eavesdropping on Trump.

On the Fox & Friends programme, Napolitano, a political commentator and former New Jersey judge, said that rather than ordering US agencies to spy on Trump, Obama obtained transcripts of Trump's conversations from Britain's Government Communications Headquarters (GCHQ), the equivalent of the US National Security Agency (NSA), which monitors overseas electronic communications.

“Three intelligence sources have informed Fox News that President Obama went outside the chain of command - he didn't use the NSA, he didn't use the CIA, he didn't use the FBI and he didn't use the Department of Justice,” Napolitano said, adding that the former president “used GCHQ.”

GCHQ has a close relationship with the NSA, as well as with the eavesdropping agencies of Australia, Canada and New Zealand in a consortium called “Five Eyes.”The British official said that under British law, GCHQ “can only gather intelligence for national security purposes” and noted that the US election “clearly doesn't meet that criteria.”

The official added that GCHQ “can only carry out intelligence operations where it is legal in both the US and UK to do so.”

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Under US law, presidents cannot direct wiretapping. Instead, the federal government can ask a court to authorise the action, but it must provide justification.

The British agency declined a request for comment.