Keir Starmer is set to reveal radical plans to scrap the unelected and "indefensible" House of Lords if Labour wins power.
In a major speech, the Labour leader will vow to deliver "the biggest ever transfer of power from Westminster to the British people".
Promising far-reaching reforms, he will say: "Britain will see a change not just in who governs but how we are governed".
Getting rid of the Lords will be one of 40 recommendations included in the Commission on the UK's Future report Mr Starmer set up in 2020.
Published on Monday the report will propose a democratically elected Assembly of Nations and Regions to act as "custodians of change".
The Mirror has had a long-running campaign to abolish the unelected Lords.
The 155-page report calls for the creation of a citizens' jury to oversee the system and whether "enforcement of it is to the public's satisfaction".
The work has been spearheaded by the ex-Prime Minister Gordon Brown who tonight blasted the bloated size of the upper chamber.
He said: "The current House of Lords is indefensible.
"Every second chamber in the world, with very few exceptions, is relatively small and usually smaller than the first chamber. And we've now got a House of Lords that has got 830 members.
"That is compared with the American senate which has 100 members to cover 300 million people - we have got a House of Lords which is 800-plus to cover only 60 million people."
The Commission will also recommend new rules to end "the undue influence of wealth and foreign money, and prevent MPs part-timing the job".
Mr Brown suggested last night this would amount to a ban on MPs' second jobs but indicated there could be exemptions for those who need to maintain professional qualifications such as doctors and nurses.
Other key planks will include handing new powers over transport and housing to mayors and local authorities across the country.
The report will suggest transferring resources out of Westminster by sending 50,000 civil servants to "work directly for communities".
The former Labour PM Mr Brown, who will appear alongside Mr Starmer tomorrow, said the proposals will answer "people's desire for change".
Mr Starmer will add: "People know Britain needs change. But they are never going to get it from the Tories. I am determined that, with Labour, people will get the change they deserve".
