Just imagine, for a nano second, what would happen if Labor’s Bill Shorten proposed a referendum to change Australia’s flag.

He would be carved up by many on the conservative side of politics, denounced for attacking a sacred national symbol.

It is too absurd to even hypothesise about Tony Abbott suggesting a new flag. The Howard government brought in legislation to give maximum protection to the existing one.

Yet in New Zealand Abbott’s counterpart, Prime Minister John Key, leader of the National Party, is arguing for the replacement of that country’s flag, which is very similar to Australia’s.

In a major speech on the issue on Tuesday, he promised a referendum on altering the flag if he is re-elected.

Key, who has just announced the NZ election will be in September (remember when Julia Gillard gave that sort of notice?), said that once next year’s centenary of Gallipoli had passed, “it will be time for us to take some decisions about how we present ourselves to the world beyond 2015”.

“The current flag represents the thinking by and about a young country moving from the 1800s to the 1900s,” he said.

“It’s my belief, and I think one increasingly shared by many New Zealanders, that the design of the New Zealand flag symbolises a colonial and post-colonial era whose time has passed. The flag remains dominated by the Union Jack in a way that we ourselves are no longer dominated by the United Kingdom.”

Contrast Abbott’s comments on the Australian flag in 2010: “I think it represents our history and I think it represents our future”.

Notably, Key’s argument for change is accompanied by his support for NZ keeping its tie to the monarchy.

“Our status as a constitutional monarchy continues to serve us well. It’s an arrangement that provides stability, continuity and keeps our head of State above party politics.” He rejects the argument that the flag should be looked at only if wider constitutional arrangements are being reviewed.

In Australia the (at present dormant) republic debate has been seen as the important one, ahead of the flag issue (although if there were an Australian republic, pressure would come on to change the flag, not least because it includes the Union Jack).

One strong criticism levelled against those who have advocated a new flag here is that so many Australians fought and died under the existing one. Those representing returned service men and women in NZ mount the same case.

But Key said that “being respectful of our history does not lock us permanently in the past” and uses the military milepost to support his case.

The centenary would be marked with the present flag, he said, but as New Zealanders reflected on past and future in that context, it was “an appropriate time to write one small but significant new chapter in our national story by reconsidering the flag”.

Key is seeking to make the centenary a focal point for some new thinking about asserting Kiwi identity.

He proposes setting up a cross party group to oversee the flag consideration process, stressing that “all voices need an opportunity to be heard”. He doesn’t underestimate the resistance to change – although Labour is on board – admitting it is “very possible” that the outcome of the process will be the present flag stays.

Key’s own preference is for the country’s silver fern as a new flag. That is on NZ war graves abroad. But he said he was open to other designs.

“We want a design that says ‘New Zealand’ in the same way that the maple leaf says ‘Canada’, or the Union Jack says ‘Britain’, without a word being spoken, or a bar of those countries’ anthems being heard.”

That New Zealand is considering a flag change doesn’t mean Australia should necessarily follow suit. There are persuasive arguments both ways on the flag, including the advantage of historical continuity.

But what John Key is doing should be kept in mind next time some Australian political figure suggests that anyone who urges a a new flag is unpatriotic or worse.

 Michelle Grattan is Professorial Fellow at the University of Canberra.

This article was first published at The Conversation.