The process for electing a new Archbishop of Canterbury has become an “omnishambles”, members of the General Synod said after cardinals in the Vatican took just two days of deliberations to pick a new pope.

The conclave to choose a successor to Pope Francis began on Wednesday, 16 days after his death on April 21. The selection of Cardinal Robert Prevost, who will be known as Pope Leo XIV, was confirmed on Thursday..

Six months after Justin Welby announced his resignation as Archbishop of Canterbury and four months after he vacated the role, the Church of England is still struggling to select the 17 members it needs to make up the crown nominations commission (CNC),which will choose his successor.

Some church lawmakers have questioned whether the aim of announcing a new archbishop by this autumn, almost a year after Welby’s announcement, will be met.

The full line-up of 17 electors was meant to be announced in March, but the last three spots, to be taken by representatives from the diocese of Canterbury, remain unfilled.

Officials from the diocese met on Tuesday night and decided they would have to rerun the process for electing a vacancy-in-see committee for the diocese. This committee is a body of more than two dozen local priests and lay people elected by members of Canterbury’s local synod, three of whom will be elected to sit on the CNC.

There were concerns that the committee’s original selection process, which concluded in March, may have been bungled by those running the election for the diocese. The names of people who were due to be elected unopposed were wrongly included on ballot papers, which is thought to have caused problems with the single transferable vote system.

It is understood that diocesan officials have been seeking legal advice,with the church keen to ensure the integrity of the electoral process. A rerun is likely totake weeks.

Amanda Robbie, a lay member of the General Synod, said: “The election of the new pope is all systems go. Meanwhile, the Church of England’s process to elect a new Archbishop of Canterbury continues to be an omnishambles.”

A papal conclave restricts voting to cardinals aged under 80. By contrast, bishops, priests and lay people play a role in the election of a Church of England archbishop, which also includes public consultations. More than 11,000 people have engaged with the process this year.

The rules have changed since Welby’s election in 2012 to include more overseas representatives and ensure female representation.

Helen King, another synod member, said it was “entirely right” that the Church involves lay people, but added: “The conclave is making our church members ask just where the process of finding a new Archbishop of Canterbury is now. The answer is that we don’t know.

“The process should be transparent but that hasn’t been the case and we don’t even know who will be making the decision. It makes me wonder whether the original intention of having a new archbishop by the autumn can still be met.”

The CNC will include the Archbishop of York and the Bishop of Norwich and be chaired by Lord Evans of Weardale, the former head of MI5.

It is understood that another 11 members have been elected but not yet announced, including five from Anglican churches overseas and six from the General Synod. The identities of four of the synod members can be surmised because they are set to be elected unopposed.

The commission was due to hold its first meeting in May to start drawing up a shortlist of bishops to interview. Insiders have said that this is still the aim, but it depends on how quickly the final three representatives from Canterbury can be named.

The CNC will hold a second meeting in July and a final one in September. Those in charge of the process hope this will remain the timetable.

The Rev Marcus Walker, rector of St Bartholomew the Great in London, described the situation as “ridiculous”, saying: “Over the last few decades, the church has surrendered to a managerialism they were convinced would secure its salvation in the modern world. The trouble is the managerial church cannot manage its way out of a paper bag.”

Walker added that the conclave makes the Church of England’s process “look even more sclerotic and bureaucratic”.

Robbie said: “It’s embarrassing. The Church of England is quite amateurish in a lot of the ways it does things.”