Dominic Cummings has said removing Boris Johnson from power is “an unpleasant but necessary job” similar to “fixing the drains”.
In an interview with New York magazine, the prime minister’s former chief adviser dismissed Johnson as a “complete fuckwit”.
It comes as Johnson’s future hangs in the balance as he awaits the delivery of Sue Gray’s report into parties in No.10 during lockdown.
Tory MPs could move to oust him as leader by triggering a no confidence vote if the results of her inquiry land badly.
Cummings said Johnson was now “rattling around in there [No.10] and fucking everything up for everyone and not doing the job properly”.
He also accused the prime minister of having being obsessed with whether Big Ben and told Cummings he was the “fucking king around here and I’m going to do what I want”.
“I was sitting in No.10 with Boris and the complete fuckwit is just babbling on about: ‘Will Big Ben bong for Brexit on the 31st of January?’ He goes on and on about this day after day,” Cummings said.
In the lengthy interview, Cummings accused Johnson of thinking of himself as “a Roman emperor”.
“The only thing he was really interested in — genuinely excited about — was, like, looking at maps. Where could he order the building of things?” Cummings said.
Cummings worked in Downing Street until November 2020 and has launched a series of attacks on Johnson since leaving.
He has also played a key role in publicly highlighting allegations about gatherings in No.10 that could have broken Covid rules.
Cummings has said he is willing to “swear under oath” Johnson lied when claiming he did not know in advance that a May 20, 2020 gathering would be a “drinks party”.