Dominic Cummings has claimed a female Downing Street worker said Boris Johnson "just stares at our t*ts" during his time as prime minister.
Johnson's final few weeks in office are set to be dogged by accusations that he presided over a culture of misogyny and drinking while in the top job.
In an ITV programme Tonight: Boris Johnson: The Rise and Fall that aired on Thursday night an anonymous source who worked at No 10 claimed that the Johnson administration had "a very masculine culture" that was "uncomfortable" for women to work in.
However, Number 10 communications chief Guto Harri claimed in the programme that Johnson had "carried the can for the bad behaviour of others" and blamed former aides for creating the culture.
He said: "Previous aides who have devoted their lives to bringing down the PM did indeed preside over a nasty, misogynist culture.
"Downing Street has been a much better place without them."
Cummings, Johnson's former right hand man and the likely target of Harri's comments, responded by accusing the prime minister of being involved in such behaviour.
He tweeted: "As one young woman forced out by (Johnson) said, 'he just stares at our t**s'. (Johnson) has decades of nightmare history with women, he hired shockers who drove junior women out of no10, & has now got his (Johnson) spin doctor pretending HE is the real victim! A disgraceful 6 week exit coming..."
He added that Johnson had hired individuals that forced junior women out of their roles.
It is not the first time Cummings has made similar allegations, having wrote in a blog post in November that a woman who worked closely with Johnson while he was PM told him: "He can’t take women seriously, he can’t help staring at t**s and talking like we’re idiots."
Cummings, who left No 10 in acrimony in November 2019, has not provided any evidence to support his claims. He has spent the last 12 months openly seeking to discredit Johnson and undermine him.
Allegations of an inappropriate drinking culture were also contained in the Sue Gray report, which was released in full in May. It found there was a culture of drinking and partying inside Downing Street, even during months where strict lockdown restrictions were in place.
In what appeared to be a criticism towards the prime minister and senior civil servants, Gray said in her report: “The senior leadership at the centre, both political and official, must bear responsibility for this culture.”
In the ITV documentary, a number of other claims were made by an aide speaking anonymously to the programme.
He said Johnson was "completely disorganised" and would not read his notes, adding: "First thing in the morning Boris Johnson would turn up two hours late. “His hair would be wet. He'd have like his zip undone or his shirt hanging out. He'd be just a complete mess all the time."
Yahoo News UK has contacted Downing Street for comment.