The PM has come under fire after comments he wrote in right-leaning magazine Spectator re-emerged in which he branded the children of single mothers "ill-raised, ignorant, aggressive and illegitimate".
He made public his view in a 1995 issue of the magazine which he went on to edit, and was accused by Labour of showing "contempt for women and families".
The Labour Party criticised Mr Johnson's attitude towards women, highlighting comments he made in articles written in 1995, 2001 and 2005, which Labour says are "sexist and misogynistic".
In the 1995 column dug up by Labour researchers, the Prime Minister said it was "outrageous that married couples should on average be forking out £1,500 in tax to fund the single mothers' desire to procreate independently of men".
He also suggested that that the modern Briton (a man) is "feeble" if he is unable to "restore women's desire to be married" and "to take control of his woman and be head of a household."
It came after Mr Johnson paid tribute to Nancy Astor, the first female MP to take her seat in the House of Commons, ahead of an unveiling of her statue in the Plymouth on Thursday,
The Prime Minister said: "When Nancy Astor entered Parliament 100 years ago, she was a trailblazer, ripping up the conventions that held women back from joining the workplace.
"A Conservative majority government will support women to reach their full potential - be that in the workplace, by opening up new opportunities to work flexibly or start their own business, or through our work internationally to make sure all young women get 12 years of education."
Shami Chakrabarti, Labour’s shadow attorney general, accused Mr Johnson of attacking single mothers and unmarried woman as well as advocating sexual harassment.
She said: “These unearthed comments further reveal Boris Johnson’s contempt for women and families, as he hypocritically attacks what he appallingly describes as 'illegitimate' children.
“His sexist comments are an affront to women everywhere. He has no right to attend or have any involvement in this event," she said.
"Someone whose attitudes towards women are straight out of the dark ages is not fit to be Prime Minister of our country.”
Mr Johnson also wrote in the 1995 article that children of single mothers are “ill-raised, ignorant, aggressive and illegitimate children who in theory will be paying for our pensions”.
As a way of tackling teen pregnancy he said: “It must be generally plausible that if having a baby out of wedlock meant surefire destitution on a Victorian scale, young girls might indeed think twice about having a baby."
“And yet no government – and certainly no Labour government – will have the courage to make the cuts in the safety net of the viciousness required to provide anything like such a deterrent.
"For the reality, surely, is that nine times out of 10 these girls will go on having babies out of wedlock not because they want to qualify for some state hand-out, but because, in their monotonous and depressing lives, they want a little creature to love.”
In a 2001 column, Mr Johnson also described what he calls the "Tottometer" as a way to measure the attractiveness of women.
He wrote: “It is what is called the Tottometer, the geigercounter that detects good-looking women. In 1997, I reported, these were to be found in numbers at the Labour conference. Now – and this is not merely my own opinion – the Tories are fighting back in a big way.”
Describing the wife of William Hague he wrote: "Everyone's personal Tottometer was squeaking away like crazy when Ffion Hague came round our tables, and I leapt to my feet to kiss her."
In a third article, from 2005, the Prime Minister described a woman at the Spectator office called "Kimberly" waking him up from a nap.
He wrote: “Relax. It’s only Kimberly, with some helpful suggestions for boosting circulation. Just pat her on the bottom and send her on her way.”
Baroness Chakrabarti said on Wednesday night that the 2005 article, while tongue-in-cheek in tone, effectively advocated workplace sexual harassment.
The Conservative Party have been contacted for comment.