She criticised the decision to keep the two-child benefit cap and means-test the winter fuel payment, and accused the prime minister of “hypocrisy” over his acceptance of free gifts from donors.
“Since the change of government in July, the revelations of hypocrisy have been staggering and increasingly outrageous,” she said.
“I cannot put into words how angry I and my colleagues are at your total lack of understanding about how you have made us all appear.”
Ms Duffield also mentioned the recent “treatment of Diane Abbott”, who said she thought she had been barred from standing by Labour ahead of the general election, before Sir Keir said she would be allowed to defend her Hackney North and Stoke Newington seat for the party.
Her relationship with the Labour leadership has long been strained and her decision to quit the party comes after seven other Labour MPs were suspended for rebelling by voting for a motion calling for the two-child benefit cap to be abolished.
“Someone with far-above-average wealth choosing to keep the Conservatives’ two-child limit to benefit payments which entrenches children in poverty, while inexplicably accepting expensive personal gifts of designer suits and glasses costing more than most of those people can grasp – this is entirely undeserving of holding the title of Labour prime minister,” she said.
Ms Duffield said she will continue to represent her constituents as an independent MP, “guided by my core Labour values”.
The resignation caused friction on social media after Nottingham East MP Nadia Whittome, who appeared to disagree with Ms Duffield’s views on opposing transgender reforms, posted that the party should have removed the whip from her “long ago”.
Writing on X, Ms Whittome said: “No matter your views on her stated reasons for quitting, Rosie Duffield has made a political career out of dehumanising one of the most marginalised groups in society
“She should never have been allowed the privilege of resigning. Labour should have withdrawn the whip long ago.”
But jumping to Ms Duffield’s defence was Harry Potter author JK Rowling, who described the MP as “one of the few female Labour politicians with guts to stand up for vulnerable women and girls”.
“Keep her name out of your mouth,” the author, who has been widely condemned in recent years for her views on transgender rights, directed at Ms Whittome.