Assistant Minister Andrew Leigh is a rarity in the federal Labor caucus, being aligned to neither the left nor the right faction.

Dr Leigh will set out his argument in a speech to the Per Capital John Cain lunch in Melbourne on Wednesday, a month out from Labor’s national conference.

“Across the country, the power of the factions is at an all-time high,” the Canberra-based MP will say.

“We need to ensure that it is a legitimate choice for everyone – from new members to elected officials – to be non-factional.

“To join Labor should be enough.”

Highly formalised factions began in the early 1970s and they now control the ALP’s national executive and allocate positions in the federal ministry.

They also determine the agenda of the national conference, decide almost all preselections, and Dr Leigh says they even choose who will travel on international parliamentary delegations.

Dr Leigh will say factions have played a role in providing stability to the party, reducing internal dissent and diversifying its membership, especially in the federal caucus.

But there are a number of reasons to be concerned if the party is dominated by factions.

“When both factions see it as desirable to find a ‘fix’, debate can be viewed as unhealthy,” Dr Leigh will say.

“Calling a truce in the battle of ideas is not the Labor way.

“If we stifle internal debate, we miss the chance to test our policies among ourselves, and to train new generations of thinkers.”

Factions also undermine the principle of the secret ballot, and the way in which preselections are run can result in failing to choose genuine, local candidates.

Also, people seeking to become grass-roots members of the ALP could be put off by being made to feel unworthy by faction members.

“As Chifley’s ‘Light on the Hill’ speech so powerfully articulated, most Labor members join ‘not hoping for any advantage from the movement, not hoping for any personal gain, but because you believe in a movement that has been built up to bring better conditions to the people’,” Dr Leigh will say.

He will say non-factional members would not “engage in the kind of antics that led to a 60 Minutes expose and an inquiry by the Victorian anti-corruption commission”.

“They would no more dream of using pre-paid gift cards to subvert branch-stacking rules than they would imagine voting for One Nation,” Dr Leigh will say.

“They joined Labor to shape a better nation. They should not be treated as second-class citizens within our party.”