MP Louise Ellman has quit the Labour Party, saying Jeremy Corbyn is “not fit” to become prime minister.
The Liverpool Riverside MP said in a letter she had been “deeply troubled” by the “growth of anti-Semitism” in Labour in recent years.
Mrs Ellman, who is Jewish, has been a party member for 55 years but said she “can no longer advocate voting Labour when it risks Corbyn becoming PM”.
Labour said it was taking “robust action” to root out anti-Semitism.
Mrs Ellman, who has been an MP since 1997, said anti-Semitism had become “mainstream” in Labour under Mr Corbyn’s leadership.
“I believe that Jeremy Corbyn is not fit to serve as our prime minister,” she said.
“With a looming general election and the possibility of him becoming prime minister, I feel I have to take a stand.”