Veteran MP Dame Louise Ellman quit Labour last night, accusing Jeremy Corbyn of being a danger to Britain.
Dame Louise, 73, who is Jewish, said she had been "deeply troubled" by the "growth of anti-Semitism" in Labour in recent years.
And she told The Times newspaper that if he became prime minister "I believe that Jeremy Corbyn would be a danger to the country, a danger to the Jewish community as well, but a danger to the country too".
Yorkshire Labour MPs have reacted to her announcement with shock and strong words.
Yvette Cooper, MP for Normanton, Pontefract and Castleford , said this morning: “No words or tweets work. [I] am just despairing at [the] way Louise Ellman has been treated and am sickened to the stomach at [the] response from some in our party to her resignation.
“Louise has been a strong, brilliant, principled Labour MP for over 20 years - it shames us all that we’ve lost her.”
While Dan Jarvis, MP for Barnsley Central, said “this must be yet another wake-up call” to the party.
He said: “I am deeply saddened that my Parliamentary colleague Louise Ellman has decided to leave the Labour Party. She has been a dedicated elected representative for almost 50 years and it is a matter of profound shame that she feels no longer able to serve as a Labour MP.
“This must be yet another wake-up call to the Labour Party that we need to do more to eradicate the scourge of anti-Semitism from our movement.”
Rachel Reeves, MP for Leeds West, tweeted: “Our party should hang its head in shame that you have left us tonight.”
While Halifax MP Holly Lynch called it “a devastating loss to the Labour Party”.
Kevin Barron, MP for Rother Valley said it was a “sad day for Labour” while Don Valley MP Caroline Flint and Rotherham MP Sarah Champion also said they were sad to see her leave.
In a statement, Dame Louise said she felt Labour was not a safe place for Jewish people.
She said: "Under Jeremy Corbyn's leadership, anti-Semitism has become mainstream in the Labour Party. Jewish members have been bullied, abused and driven out.
"The Labour Party is no longer a safe place for Jews and Jeremy Corbyn must bear the responsibility for this.
"We cannot allow him to do to the country what he has done to the Labour Party.
"The overwhelming majority of the Jewish community is fearful of what a Corbyn government might mean for Britain's Jews. I share those concerns.
"But this issue is not simply about the Jewish community. This is about the nature of our society.
"Jeremy Corbyn's seeming tolerance of anti-Semitism would embolden racists, poison our public debate and damage the social cohesion of our country.
"My values - traditional Labour values - have remained the same. It is Labour, under Jeremy Corbyn, that has changed.”
A Labour Party spokesperson said: "Jeremy Corbyn thanks Louise Ellman for her service to the Labour Party over many years.
“Jeremy Corbyn and the Labour Party are fully committed to the support, defence and celebration of the Jewish community and continue to take robust action to root out anti-Semitism in the party and wider society.
"Jeremy Corbyn has consistently supported struggles for human rights and justice around the world and made the right calls in the interests of security and peace."