Momentum is to launch a nationwide campaign to encourage members to begin deselection processes for Labour MPs, arguing it can open the door for more diverse, younger, working-class MPs.

The grassroots group said it would support rank-and-file members across the country to begin the process of challenging their sitting MP under Labour’s trigger ballot system.

The system, which was changed last September to make it easier for local party members to challenge MPs, allows members to vote on whether they would like their sitting MP to face a full selection process or be automatically reselected.

If more than a third of local party branches or more than a third of affiliate branches are in favour of open selection, a reselection process will take place where other candidates can challenge the MPs for the seat.

Momentum said the drive was influenced by the ongoing Tory leadership race, which it called a “broken political system dominated by posh men from expensive private schools”.

“For too long an outdated rulebook and a culture of deference have meant an absence of democracy and accountability across the party,” the group said in a statement.

“As two privately educated millionaires battle for the votes of an overwhelmingly white, wealthy Tory membership to become the next prime minister, the rising stars of the Labour party must look and sound very different.”

Momentum said a fully open procedure would help heal the alienation that many ordinary voters felt.

“Campaigning for open selections across the country will help surface a new generation of young, BAME, working-class leaders who will take on the political establishment and provide a genuine alternative,” the group said.

“We must remember that our strength lies in the knowledge and talent of Labour’s half a million members who live and work in every community. Collectively, they understand the damage wrought by decades of neoliberalism. They know we need a bold, radical agenda in government to rebuild communities, take on the establishment and avert climate disaster.

“They are the kind of people we need as Labour MPs in a Corbyn-led government, and Momentum will support its members to push for open selections across the country and give this new generation a shot at parliament.”

The group said it would support a number of working-class and diverse candidates in target seats, including Ali Milani, the 24-year-old former NUS officer running against Boris Johnson, the thinktank boss Faiza Shaheen, running against Iain Duncan Smith in Chingford and Woodford Green, and Sonya Ward, a former youth worker who is aiming to retake the traditional Labour seat of Mansfield, which was won by the Tories in 2017.

Earlier this week, Labour’s ruling national executive committee said pregnant MPs would only be subject to a trigger ballot process one year after their return from maternity leave and would be automatically reselected if a snap election occurred within a year.

Harriet Harman had asked for pregnant MPs and new mothers to be protected for the whole of the parliament, after it emerged that a member in Ellie Reeves’s Lewisham West and Penge constituency was planning to put forward a motion of no confidence in her, which was ultimately dropped. Reeves is five months pregnant.

For other MPs, the process for trigger ballots could begin taking place from September, after the party asked all MPs to confirm whether they would stand again at the next election.