Ed Miliband has been accused of paying "lip service" to the principle of House of Lords reform as he set out plans to abolish the upper chamber and replace it with an elected senate.
The Labour leader has said that he wants to ensure the new body properly represents all the towns, cities, regions and nations that make up the United Kingdom.
But the plans drew an angry response from the Liberal Democrats who bitterly accused Labour of combining with Conservative MPs to wreck their plans to reform the Lords two years ago.
"Ed Miliband partnered up with backbench Tories to destroy the best chance this country has had to reform the Lords," said Lib Dem deputy leader Sir Malcolm Bruce.
"We could have given the UK greater representation in Parliament, but when presented with the chance, he bottled it; turned his back and ran.
"This is simply lip-service from a Labour party who have no intention of actually delivering."
Labour said that it would summon a constitutional convention early in the next parliament to consider how an elected senate would be established - including whether it could have specific regional representation functions.
Each region of England, as well as the devolved administrations of Scotland, Wales, and Northern Ireland, would hold meetings before the convention where people would be asked for views on the functions of the new body, as well as the most appropriate form of election.
In a speech to activists in Blackpool, Mr Miliband will say: "It cannot be right that the North West has almost the same population as London but only a small fraction of London's number of peers.
"London is our capital and one of the world's great cities but it cannot be right London has more members of the House of Lords than the East Midlands, West Midlands, Wales, Northern Ireland, the North East and Yorkshire and Humber added together.
"And it cannot be right that those peers who do live outside London are less likely to be from great cities like Birmingham, Liverpool and Bristol than they are to be living in less-populated rural areas.
"We will make the second chamber of Parliament truly a senate of the regions and nations of our whole country."