Labour has failed its core voters on immigration and public services, leading rebel Frank Field will say later today.
The former welfare minister and leader of the backbench rebels responsible for Gordon Brown's humiliating 10p income tax U-turn will make the claim in a lecture at the University of Hertfordshire, where he is chancellor.
Mr Field believes Labour is in the same position as the doomed Liberal party, which went into terminal decline after the first world war.
"Labour has failed to represent its core vote on two issues which these voters put towards the top of their agenda," he will say.
"It has allowed uncontrolled immigration with its impact not just on earnings but more generally on housing, schools and other public services, to the disadvantage of working class English voters, both white and black."
He will warn the British National party (BNP) could prove attractive to many core Labour voters, both on immigration and on Labour's failure to address unresolved devolution issues.
Mr Field wants the prime minister to lead efforts to give greater independence to England, which many fear is underrepresented at parliament. Issues affecting it are voted on by Scottish and Welsh MPs, but English MPs do not have a say over affairs in devolved areas.
"Just as it was conventional wisdom that the Tories were best placed to enact decolonisation so, similarly, will a Scottish prime minister be best placed to resolve the English question," Mr Field will say.
"By initiating a debate, and admitting that at this stage no one quite knows where the process will lead, Gordon Brown would both set some of the parameters as well as the speed of the debate."
Ultimately a failure to address the issue could lead to electoral disaster, Mr Field adds.
He says the English question is "a real threat which could all too easily have a catastrophic impact on the party's ability to challenge for power in England".