He claimed that rather than ordering US agencies to spy on Mr Trump, Mr Obama obtained transcripts of Mr Trump's conversations from Britain's GCHQ, which monitors overseas electronic communications.

Mr Spicer read out the report, quoting Mr Napolitano.

"Last on Fox News, on March 14th, Judge Andrew Napolitano made the following statement, quote, '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. He used GCHQ. What is that? It's the initials for the British intelligence finding agency. So, simply by having two people saying to them president needs transcripts of conversations involving candidate Trump's conversations, involving president-elect Trump, he's able to get it and there's no American fingerprints on this. Putting the published accounts and common-sense together, this leads to a lot.'"

GCHQ has a close relationship with its American equivalent, the NSA, as well as with the eavesdropping agencies of Australia, Canada and New Zealand in a consortium called "Five Eyes".

British officials were quick to rubbish Mr Napolitano's claims earlier this week. A government source reportedly said the claim was "totally untrue and quite frankly absurd".