Labour would replace the House of Lords with an elected senate if the party won next May's general election, party leader Ed Miliband has said.
He told a conference in Blackpool on Saturday the current system "fails to represent large parts of the UK".
Senators would be elected from Scotland, Wales, Northern Ireland and the English regions instead of from constituencies like MPs.
This will give the senate a "clearly defined different role", Labour says.
Mr Miliband said the issue was not just constitutional, but economic, social and one of fairness.
'A Britain that works for all'
He added: "We need to do so much more to reverse a century of centralisation that we've seen in our country.
"The House of Lords is one of the biggest pieces of unfinished business in our constitution.
"The North West has nearly the same population as London, but five times more members of the House of Lords are from London than from the North West.
"London has more members in the House of Lords than the East Midlands, West Midlands, Wales, Northern Ireland, the North East and Yorkshire and Humber added together.
"No wonder the recovery isn't working for most parts of Britain when the voices of most parts of Britain aren't being heard.
"It's time to reform the way we're governed, it's time every part of our country had a voice at the heart of our politics, it's time to have a senate of the nations and regions which serves our whole country so that we can truly build a Britain that works for all and not just for some."
But the Liberal Democrats have accused Labour of joining forces with Conservative MPs two years ago to wreck their plans to reform the Lords.
The Liberal Democrats wanted to change the make-up of the Lords by seeing 80% of peers elected and the total number of members halved to 450.
Lib Dem deputy leader Sir Malcolm Bruce said: "Ed Miliband partnered up with backbench Tories to destroy the best chance this country has had to reform the Lords.
"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."
Mr Miliband's announcement is part of a wider effort by Labour to pursue a policy of devolving power from Westminster.
He has said he would like a "constitutional convention" after the elections to discuss devolution plans for England.