A recent British ambassador to Washington, Sir Peter Westmacott, has criticised Donald Trump's inner circle for "peddling falsehoods" and harming shared efforts to counter terrorism.
Intelligence ties between the US and UK have been strained by claims made by the presidential press secretary, Sean Spicer, that GCHQ had helped the previous president spy on Donald Trump.
It led to US officials making an apology for repeating the claims which had been initially made on Fox News.
GCHQ issued a terse 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."
Ambassador until 2016, Westmacott wrote in the Guardian: "This is a dangerous game. The intelligence relationship between Britain and America is unique and precious.
"Peddling falsehoods and then doing nothing to set the record straight would be a gift to our enemies they could only dream of."
It comes amid reports that a new head of GCHQ has been appointed. Deputy-director of MI5, Jeremy Fleming, is said to be taking over Robert Hannigan as the head of the British intelligence agency.
Fleming has been with MI5 for 20 years with a source telling the Sunday Times that he had a "personable style and was easy to worth with.
"Jeremy will be expected to make a trip to the US very early on to seek reassurances from our partners.
"I don't think the rubbish being uttered by the Trump camp will affect the day-to-day operational co-operation between the UK and US intelligence agencies, but it'll be important to remind our partners there that more consideration and respect need to be afforded to the intelligence communities by the Trump administration," the source added.
On Monday (20 March) FBI director James Comey and NSA head Mike Rogers will testify before the US intelligence committee over the claims of wiretapping or surveillance at Trump Tower.
Meanwhile, the Foreign Secretary Boris Johnson will go to Washington this week to meet aides to Trump and senior congressional leaders.
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