A Labour MP has complained of being subjected to "vile abuse" after rebelling against Jeremy Corbyn's leadership in a parliamentary vote on the Government's fiscal charter.
Hyndburn MP Graham Jones was an opposition whip under Ed Miliband but quit the post when Mr Corbyn was elected earlier this year.
Mr Jones told BBC Radio 4's World at One that the left-winger's election had been accompanied by an influx of new members, some of whom came from "pretty unpleasant political spheres".
If MPs from the party's more moderate wing were deselected, then Labour would be "finished" he warned.
Mr Jones urged Mr Corbyn to change course on the economy, welfare and immigration, and warned a new leader would be needed if he showed himself unable to win votes in middle England.
"We are here to win elections and Jeremy and all of us will be judged on our success," Mr Jones said.
"If he can't succeed, if he can't win in areas in the shires, then it would inevitably be time for somebody else.
"I think the jury's out. I don't think in the public there's a sweeping appetite for what's being proposed.
"He has to come forward with something constructive to offer this middle England socially conservative vote so they can believe in the Labour Party, vote for us and give us a Labour government."
Mr Jones said Mr Corbyn's policy adviser Andrew Fisher had been "exceedingly disloyal" in tweets criticising Labour figures and "in an ideal world" should have been removed from the leader's office during an investigation into whether he backed a candidate from Class War in the general election.
He said the left-wing Momentum grouping was "disruptive", warning: "It's setting up two parties, effectively. I think it's a dysfunctional set-up."
Mr Jones said his local party had lost four long-standing members because of Mr Corbyn's leadership and had found that hundreds of new members and supporters who signed up in order to vote in the leadership election appeared unwilling to get involved in grassroots politics.
Following his abstention in last month's vote on the fiscal charter, he said he received "some vile abuse and it was quite fervent. Some of it was just pure bile".
Mr Jones warned: "I think the party has to be very careful.
"We are entering new territory with a broader membership base and members being drawn from some pretty unpleasant political spheres.
"I think we've got to be mindful that these people are advised to desist or removed from the membership.
"I think Jeremy needs to do a lot more.I don't think he's fully aware that this type of behaviour is as virulent and vile as it actually is.
"I want to see him change some of his policies. I think we need to be fiscally more responsible. We've got to stop turning our back on the debate on immigration. On welfare, are we just leaving people to a lifetime on benefits?"
Corbyn-supporting MP Richard Burgon told World at One that Mr Jones's complaints were "a bit of a distraction".
Mr Burgon said: "I think we all need to get behind the Labour leader who's been elected with a huge mandate - the biggest mandate that a leader of any political party has ever had.
"I don't believe there's a vile atmosphere. I believe and I know that the vast majority of Labour members and supporters want the party in Parliament to get behind Jeremy Corbyn. The good news is that most Labour MPs are behind Jeremy Corbyn."