Labour is "adrift" and has lost its connection with traditional supporters, David Lammy has said, arguing the Rochester tweet snobbery row was a symptom of a much wider problem.
The London mayoral hopeful, who previously told The Huffington Post UK that Ed Miliband would not win a majority next year, said politicians from "liberal, professional backgrounds" found it hard to identify with ordinary working people, after Labour came third in the Rochester and Strood by-election and Ukip is threatening to make inroads into the party's traditional heartlands elsewhere.
Emily Thornberry resigned from the shadow cabinet after tweeting an image of a house with three English flags and a white van parked outside on election day, with the words "image from Rochester".
The press and Ukip accused her of snobbery but Ed Miliband was accused of weakness for allowing her to resign over something minor.
But the Labour leader's efforts to move on from the scandal will be complicated by Mr Lammy's article in The Mail On Sunday.
The former universities minister Mr Lammy said that Mrs Thornberry's tweet was merely a symptom of the party's wider problem.
"We can’t allow ourselves to believe that patriotism is something to sneer at," he wrote.
"The Labour Party feels culturally adrift, not just from large parts of Britain, but from its own traditional working class base.
"Large parts of the country feel that Labour not only disagrees with them, they think we disapprove of them too.
"A sense of mutual disdain between the mainstream parties and working class England is driving voters away from politics, or towards so-called 'anti-politics' parties such as Ukip."
Mr Lammy - who grew up on a council estate close to Tottenham's infamous Broadwater Farm - argues that Labour's "discomfort hinges on immigration".
"By and large, modern Labour politicians come from liberal, professional backgrounds," he wrote.
"They have benefited from globalisation - they mix in social circles with people who work in multinational firms, enjoy foreign travel and find diversity enriching.
"Much of Labour's traditional electoral base does not feel this way ... Immigration becomes swept up in this story.
"In some areas it adds pressures to housing, or on school places. And people worry about losing a sense of community if new arrivals do not speak the language, or observe the same customs. In short, people feel that globalisation is benefiting others, but not them.
"This is what Ukip is tapping into - and Labour has to have an answer."
The Tottenham MP added: "Labour lost in Rochester and Strood not because of one tweet, but because of a growing perception that the party has lost touch with a large group of its own voters.
"That started long before Thursday. It explains why the polls show Ukip taking votes not just from the Tories but Labour too.
"People who have decent and moderate instincts are voting for a party that does not. For the sake of our country, not just our party, it is time to start putting that right."