The US has made a formal apology to Britain after the White House accused GCHQ of helping Barack Obama spy on Donald Trump.
Sean Spicer, Mr Trump's press secretary, repeated a claim on Thursday evening - initially made by an analyst on Fox News - that GCHQ was used by Mr Obama to spy on Trump Tower in the lead-up to last November's election.
The comments prompted a furious response from GCHQ, which in a break from normal practice issued a public statement: "Recent allegations made by media commentator Judge Andrew Napolitano about GCHQ being asked to conduct 'wiretapping' against the then president-elect are nonsense. They are utterly ridiculous and should be ignored."
Intelligence sources said that both Mr Spicer and General McMaster, the US National Security Adviser, have apologised over the claims. "The apology came direct from them," a source said. General McMaster contacted Mark Lyall Grant, Prime Minister Theresa May's National Security Adviser, to apologise for the comments. Mr Spicer conveyed his apology through Kim Darroch, Britain's US ambassador.
Mr Spicer had earlier repeated claims that Mr Obama used GCHQ to spy on Mr Trump before he became president. "He's able to get it and there's no American fingerprints on it," Mr Spicer said of the intelligence supposedly provided to Mr Obama by Britain.
"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."