Carrie Johnson has insisted she "plays no role in Government" and has been targeted by "enemies" of the Prime Minister in a "brutal briefing campaign".
The Prime Minister's wife issued a rare statement through her spokesperson on Sunday evening, after a Cabinet minister suggested she was coming "under scrutiny in a way that perhaps other prime ministers' spouses weren't" in the past.
Mrs Johnson's role in her husband's premiership has been under the spotlight, and over the weekend a biography of the 33-year-old mother of two, by Tory peer Lord Ashcroft, was serialised in the Daily Mail and Mail On Sunday, which sought to look at her alleged influence on the PM's decision-making.
Lord Ashcroft, writing in the Mail, said his research had suggested her "behaviour is preventing him ( Boris Johnson ) from leading Britain as effectively as the voters deserve".
But allies have dismissed the criticism as sexist, and a spokesperson for Mrs Johnson said on Sunday: "Yet again Mrs Johnson has been targeted by a brutal briefing campaign against her by enemies of her husband.
"This is just the latest attempt by bitter ex-officials to discredit her.
"She is a private individual who plays no role in Government."
It has been alleged that Mrs Johnson has been caught up in a number of scandals involving the Prime Minister, including suggestions she pushed for the luxury redecoration of the flat the couple share in No 11 Downing Street and was key in the evacuation of animals from the Nowzad charity from Kabul.
No 10 has denied Mr and Mrs Johnson had any involvement in the evacuation.
But Guto Harri, the newly appointed director of communications at Downing Street, speaking on the BBC Newscast podcast last week, said the episode "raises that other spectre that never goes away of who is influencing him (the PM) and we all know who's being accused of doing so on this occasion, because she is an animal lover more than him really".
Asked if he was referring to Mrs Johnson, he replied: "You said it, not me."
Dominic Cummings, the Prime Minister's former chief aide, has made clear he was no fan of Mrs Johnson, and said she had wanted to "get rid" of him from No 10.
He alleged she was at one point "trying to change a whole bunch of different appointments at Number 10 and appoint her friends to particular jobs".
However after his allies dubbed Mrs Johnson "Princess Nut Nut" in press briefings, David Cameron's wife Samantha said the attacks were "sexist".
She said: "In my view, your husband or partner is the Prime Minister, they're quite able to take decisions themselves, they have a huge team of advisers.
"And so the idea that it's the wife, that you're somehow influencing them over and above what they think or what advice they're getting from their team, I think it's kind of demeaning, really, for the Prime Minister."
Journalist Sarah Vine, whose divorce from Levelling Up Secretary Michael Gove was finalised last month after 20 years of marriage, said the focus on Mrs Johnson was "the equivalent of political slut shaming".
She told the BBC's Sunday Morning programme: "The trouble is, it's always the easiest thing to do to blame the woman and the truth is far more complicated than that.
"If Boris Johnson has given Carrie too much access or too much leeway, that's sort of his fault. He is the person in charge. He is the Prime Minister."
She added: "I know that the nickname Carrie Antoinette is witty and a good pun and we all love a good pun, but I just don't think her head deserves to be on the block in this way.
"Things have gone wrong and mistakes, terrible mistakes, have been made... all the partygate stuff and I agree that all of that is completely unacceptable, but it's not just her who must take responsibility for this. Ultimately, I think it's Johnson and the way he's run No 10."
Health Secretary Sajid Javid, who used to employ Mrs Johnson as a Special Advisor, said: “Going after Carrie Johnson is undignified, it is unfair and it is wrong”.
He said the weight of allegations against her was “sexist” adding: “As a general rule, a politician's partner ... should be off limits”.
Mrs Johnson’s team also denied she had secretly sent tweets and text messages from Mr Johnson's phone, after reports that aides suspected she was doing so.
One insider told the Mirror the issue was “discussed quite a bit” after Boris Johnson became Prime Minister. They said: “You could tell there was a different tone to the messages - he writes in a certain way, the way he spaces messages out. The responses would be different.”
But a source close to Mrs Johnson insisted it was false to claim she sent texts or tweets on her husband’s behalf. A spokesperson for Mrs Johnson said of the claim: “It’s just another nasty smear.”
Last month it emerged Mrs Johnson could face questions from the Met Police, who are investigating 12 lockdown gatherings in Downing Street.
Sue Gray’s report revealed Scotland Yard are looking at “a gathering in the 10 Downing Street flat” which Mr and Mrs Johnson share on 13 November 2020 - despite any such gathering being denied by both Mr and Mrs Johnson previously.
Mrs Johnson’s spokeswoman declined to comment while the matter is being investigated.
Tory minister Kwasi Kwarteng on Sunday told Times Radio: "The reportage that somehow she's got undue influence, I don't think that's true, the Prime Minister has been in politics for 25 years and has a pretty strong set of ideas."
But asked if there was an element of sexism in the treatment of Mrs Johnson compared to spouses of former prime ministers, Mr Kwarteng replied: "I wouldn't say that but I do think it's interesting when the spouse is someone in their 30s and has got open positions that are well known, people feel free to criticise - I think that's interesting."
Pressed on what he meant by "interesting", the minister replied: "I don't think it's sexist, I'm not going to go down the route of saying it's sexist but I'm saying her views are under scrutiny in a way that perhaps other prime ministers' spouses weren't."
Ms Vine said that from her own experience it was "unbelievably damaging and difficult on a personal level" when a person was "filtered through the sort of toxic filter of politics and power, and then you're made to look like something that you are actually, really genuinely not".
She said: "The mental toll on her will be significant".
Labour MP Jess Phillips has previously labelled criticism of Mrs Johnson as "sexist" and "ageist".
She said there had been briefing by "men who don't like Carrie Symonds because they don't have the influence they want to have".
She added: "I have literally seen no evidence in my day-to-day life that Carrie Symonds (has too much influence). In some regards, maybe I'd like her to have more - she's quite a feminist."
Tory MP Tracey Crouch has also spoken about how she disliked the way that Mrs Johnson had been portrayed as a Lady Macbeth figure.
While in Lord Ashcroft's book, former cabinet minister John Whittingdale, who Mrs Johnson previously worked for, said the influence she was said to have was inaccurate.
"Yes, I'm sure Boris and Carrie discuss things in a way that previous spouses would not, because they were much less political," he said.
"Samantha Cameron had little interest in politics. Philip May didn't have a great knowledge of politics.
"This is the first time the PM's wife has been a committed political activist and had knowledge and experience of working in politics, so of course it's going to be talked about. But she's very good. She advised me for 15 months, so I know she's good," he is reported to have said.
He added: "Carrie gets a tough time. It upsets her and I feel sorry for her. It's a pretty lonely existence. I think they've struggled. She doesn't see as much of Boris as she'd like because he's trying to run the country."
