The UK Labour Party's 40-point plan's centerpiece is to scrap the upper house of parliament in its current guise -- which is a mixture of political appointees, hereditary peers and Church of England bishops.
"I think the House of Lords is indefensible. Anybody who looks at the House of Lords would struggle to say that it should be kept," Labour leader Keir Starmer told British television.
"So we want to abolish the House of Lords and replace it with an elected chamber that has a really strong mission."
Brown proposed a new assembly comprising members drawn from the UK's regions and countries -- a "smaller, more representative and democratic" chamber, although details will be left to the consultation.
Labour looks set to take power in the next election, due by January 2025, streaking far ahead of the governing Conservatives in opinion polls after a tumultuous period politically and economically.
Labour leader Starmer promised "the biggest ever transfer of power from (the UK parliament in) Westminster to the British people", arguing that many voters in 2016 opted to quit the European Union because of a sense of lack of democratic control.
The party's blueprint for reform, drafted by former prime minister Gordon Brown, envisions new devolution to the UK's regions and countries including Scotland, where the nationalist government is pressing for a new referendum on independence.
Brown, who led the successful 2014 campaign for his fellow Scots to stay in the United Kingdom, proposed greater devolution, with the Edinburgh parliament included in international agreements that involve Scottish areas.
Addressing an audience in Leeds, northern England, Starmer said a "failure of economic growth over the past 12 years" under Conservative rule was caused in part by the UK failing as a whole to power growth, relying too much on London and southeast England.