Labour’s annual conference has voted in favour of proportional representation for Westminster elections – despite the policy being rejected by the party leadership.
At the weekend Sir Keir Starmer declared that electoral reform was “not a priority for me”.
But delegates backed a motion to use proportional representation at general elections anyway.
Earlier, former Labour shadow chancellor John McDonnell accused Mr Starmer of acting like a monarch over the row.
Speaking at a rally organised by the Labour for a New Democracy protest group on Sunday night, Mr McDonnell said he hoped for “constructive dialogue” with the Labour leadership.
Electoral reform also won the support of high-profile backers such as Andy Burnham.
Votes at conference are not binding on the Labour leadership, but they do make the calls more difficult to ignore.
In total, members voted in favour of three electoral reform motions, including to replace first-past-the-post with a form of proportional representation at general elections.
One of the motions stated: “Labour must make a commitment to introduce proportional representation for general elections in the next manifesto.
“During its first term in office the next Labour government must change the voting system for general elections to a form of PR.”
Mr Burnham has described the current system as “antiquated” and said it had allowed the Conservatives to spend decades in power “without ever winning a majority share of the popular vote”.
Before the vote the conference heard claims that the issue rarely came up on the dooorsteps.
Jennifer Hemingway from the Warley Constituency Labour Party told delegates she used to support a change, but now opposed it.
She said: “It is deceptive because, despite the best of principles and despite appearances, it is not as democratic in practice. It is a gift to smaller parties, some of them little more than one-issue pressure groups.”
Ms Hemingway added: “Bluntly, I have had more conversations on the doorstep about colostomy bags than about electoral reform.”
Andy Newman from the GMB union also urged the conference not to support proportional representation.
He warned: “There is an element of despair in thinking that we can’t get working class people to vote for us and that we need to abandon that project of a majority Labour government, and instead have shoddy deals with other parties.”