Labour is facing a "bloodbath" at the 2020 general election unless it adopts immigration policies more in tune with its traditional working-class support in the North and the Midlands, a major party donor has warned.
John Mills, who chaired the Labour Leave campaign in the EU referendum, warned that the party's splits over immigration and Europe threaten to create a "huge inbuilt majority" for a Conservative government in the years to come.
Mr Mills said he feared figures such as leader Jeremy Corbyn and shadow home secretary Diane Abbott were too personally wedded to "ideological purity" on freedom of movement to respond to voters' desire for greater controls.
Mr Corbyn himself was among a group of "idealists who aren't that bothered about winning elections but are worried about the purity of the Labour Party and its integrity", he said.
The party may have to wait for a new generation of more pragmatic leaders - such as Sir Keir Starmer, Clive Lewis or Dan Jarvis - to be ready to make the kind of compromises needed to build the kind of coalition which could bring Labour back to power, Mr Mills suggested.
In the short term, it risks being squeezed at the 2020 election by Ukip taking anti-immigrant votes and Liberal Democrats luring its europhile metropolitan supporters, he said.
Meanwhile, Labour MPs trying to avoid deselection are coming under pressure to adopt the pro-immigrant stance preferred by activists, even while voters are "swinging in the other direction", he added.
"The danger is that the onslaught from all these various factors is so great that there will be a real bloodbath in 2020 from which the Labour Party will struggle to recover," said Mr Mills.
"Whether it will be possible to get the show on the road to a sufficient extent to avoid bloodbath in 2020 remains to be seen."
Home shopping tycoon Mr Mills - who gave shares in his JML company to Labour - told reporters he believed most of the support for immigration control was driven not by racism or bigotry, but by concerns over competition for low-paid jobs and pressure on public services.
Many of Labour's working-class supporters would back a work permit system which allowed highly trained professionals such as doctors and scientists to continue to come to the UK, but cut back on unskilled migration from eastern Europe, he suggested.
Prominent Labour backbenchers such as Rachel Reeves and Jonathan Reynolds had responded to the public mood, he said.
But he added: "People like Jeremy Corbyn and Diane Abbott come from a very ideologically fixed firmament and have had some difficulty in adjusting to where the political realities are.
"I think their judgment is they would rather stick to some measure of ideological purity rather than compromise by swaying with the wind.
"You may say that doesn't work very well electorally, and I think you are very probably right, but I think that's where they come from."
Mr Mills warned that polls suggest Labour could "haemorrhage" voters who supported it in 2015 but backed Leave in the referendum - half of whom say they will not vote Labour again.
Some 70% of Labour-held seats - and 90% outside London and other metropolitan areas - had majorities for Leave at the referendum, he pointed out.
"This is such an electoral imperative that it is very difficult for people in the Labour Party to just push it to one side," said Mr Mills.
"There's a huge divide between the nativist approach of large numbers of Labour's working-class supporters and the more idealistic approach of their metropolitan voters."