Ian Austin has become the ninth MP to quit Labour this week, blaming leader Jeremy Corbyn for creating a culture of extremism and intolerance. He told the BBC the leadership had failed to tackle anti-Semitism and had turned the party into a narrow sect.
But the MP for Dudley North said he had no plans to join the new Independent Group of former Labour and Tory MPs. Mr Corbyn denied claims bullying was rife in Labour, telling Sky News any bad behavior had been dealt with.
Meanwhile, his deputy Tom Watson said Mr Austin's departure was a serious blow to Labour.
A Labour spokesman suggested Mr Austin should stand down and call a by-election in his West Midlands seat, which he won by only 22 votes in 2017. Mr Austin told the Express^& Star newspaper, which first broke news of his resignation, that it was the most difficult decision he had ever had to take.
The MP, who has represented the West Midlands constituency since 2005, later told BBC West Midlands that he was ashamed of the party.
I grew up listening to my dad, who was a refugee from the Holocaust, teaching me about the evils of hatred and prejudice, he said.
One of the main reasons I joined the Labour Party as a teenager here in Dudley more than 35 years ago was to fight racism and I could never have believed I would be leaving the Labour party because of racism too.
Explaining his decision not to call a by-election, Mr Austin said he had been openly critical of Mr Corbyn during the 2017 election campaign.
He said his work for the people in this community is going to carry on as it always has.
Tom Watson, Labor's deputy leader, said he was deeply saddened by his close friend decision to leave.
I didn't want him to go, not just because he is a friend but because Labour needs people of his experience, caliber and passion if we are to win, he added.
The Labour leader Corbyn told Sky News: There is no place for harshness, bullying or anything else in the party. I don't believe that it exists on a wide scale.