Littleproud said he was disappointed by Gee’s decision but accepted his departure, adding his colleague had always been free to vote his way on the Voice.

“While the Federal Nationals remain united in our decision to oppose The Voice to Parliament, I have stated from the beginning that one of the great things about our Party Room is the ability to have different opinions and speak and vote freely on issues that matter to individual members and nothing has changed,” Littleproud said in a statement.

Gee’s decision to quit the Nationals will mean Littleproud and Opposition Leader Peter Dutton will need to make minor changes to their front bench team.

The Nationals announced at a fiery press conference in November they would formally oppose the Voice to parliament, but the party had split over the issue within a day.

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Gee, who was was the minister for veterans’ affairs and defence personnel in the Morrison government, was the first to break ranks to express his support for the Voice.

The Western Australian state branch also expressed support for the referendum and former federal leader Michael McCormack said the party could reverse its position next year, depending on the details of the proposal.

Albanese described Gee’s resignation as an “extraordinary political development” that left the federal opposition with one fewer vote in the parliament.

“Andrew Gee’s statement is one of principle,” Albanese said. “I look forward to working with him and look forward with members of the Liberal Party, members of crossbenchers across the board who want to recognise, see this as an opportunity to unite our nation. That’s what it should be.

“I’m pleased that Andrew Gee will be campaigning for a yes vote, but I say to other members of parliament as well – don’t miss the opportunity to be a part of enriching our nation and making us even stronger in the future.”

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In his statement, Gee said: “I was once a true believer, but I’m not any more.

“The National Party of today is very different to the one of my youth. I feel that I can best represent the constituents of Calare and our region by speaking out on issues, free from party constraints and expectations.”

The Liberals have not yet stated whether they will support or oppose the Voice or allow their MPs a free vote.