The claim brought a rare public denial by GCHQ which described the claims as “utterly ridiculous” while Downing Street said it had secured an assurance that the allegation would not be repeated.
But at a joint news conference with German Chancellor Angela Merkel on Friday, Trump said only that Spicer had just been quoting retired judge Andrew Napolito who he described as a “very talented legal mind”.
“We said nothing,” he said. “I don’t make an opinion on it,”
Westmacott said senior US officials were well aware the president was playing a “dangerous game” which revolved around Trump’s “famous reluctance to admit mistakes” combined with his suspicion of intelligence agencies.
He warned it risked undermining a relationship that was “critical” to US-UK efforts to counter a range of threats including terrorism, Russian aggression, Chinese cyber-attacks, and the nuclear threat from North Korea.
“The intelligence relationship between Britain and America is unique and precious. It is based on unquestioned mutual trust, between operatives and politicians on each side of the Atlantic,” he said.
“That is something both countries have taken for granted since the Second World War.
“Gratuitously damaging it by peddling falsehoods and then doing nothing to set the record straight would be a gift to our enemies they could only dream of.”
Westmacott’s comments will be seen as underlining the strength of feeling among the British intelligence and diplomatic communities at the actions of the White House.