Jeremy Corbyn has provoked tensions within his party over the thorny issue of allowing those who self-identify as a woman but are still legally considered a man, to go on all-female candidate lists.
The policy has landed him in hot water with feminists from the party, including veteran campaigners like Linda Bellos.
They claim trans people who self-identify as women should not be allowed on all-women Labour candidate shortlists because it goes against efforts to promote gender diversity.
Some party members have even mounted a crowdfunding campaign in a bid to challenge the decision.
And now Mr Corbyn’s views have provoked rage on the Mumsnet website – the very audience he tried to court last year with an online Q&A session.
Members are using the hashtag #LabourLosingWomen to hit out at what they see as a male-centric view at the top of Labour.
Many claim they no longer support the party as the transgender views were the last straw.
One, Winifred, wrote: “I was a staunch Corbynite, and party activist. I have selfies of us cheek to cheek on two different occasions.
“But the scales fell from my eyes when he announced that men are women because they say so and because they are men we have to do as they say, and that means agreeing that they are women.
“I’ve struggled all my career with gender bias. Sorry Jezzer, and bye.”
One Labour member, a feminist and mother in her 40s, who campaigned for Mr Corbyn in the General Election, urged the ultra left-winger to think again as men self-identifying as a woman “are not women”.
She complained: “This is a very important issue for me and I believe for women in general.
“I cannot say with any certainty that I would still vote for Labour if self ID is brought in.
“And that is very sad for me to admit as I campaigned hard on the streets and within my own social circle to communicate Labour’s message of hope and social progress.
“I believe that JC is a principled and honest politician who truly wants to bring about a more equal society.
“I fervently hope that he is also interested in listening with an open mind to feminist concerns.”
Another user wrote: “If we are allowed to self-identify as women, what else can we self-identify as? Is this restricted to sex or can we self ID our race and age as well?
“My mother is 70 but looks 60 and always got on well with 60 yr olds. Can she have her birth certificate amended to show the age she feels? If not, why not?”
During an appearance on the Andrew Marr show last month, Mr Corbyn was challenged over the issue but insisted people who choose to declare themselves a woman “should be respected”.
He said: “The position of the party is that self-identification is what it is,” he told the Andrew Marr show today.
“The position of the party is that where you have self-identified as a woman you are treated as a woman.
“These people have been through a big decision a big process a big trauma, let’s look at the human beings in front of us.
“My mind is that I look at the person in front of me. I see that that’s their identification that should be respected.”