Sir John Key says if he could do it all over again he would not hold a referendum before changing the flag.
The former Prime Minister told 66 Magazine he believes New Zealanders would have accepted a new flag eventually.
- Sir John Key says biggest regret as PM was not changing flag
- Sir John Key a big Mark Richardson fan
- New Zealand flag debate will 'keep flaring up' until it's changed - campaigner
"I think it's one of those things that all hell would have broken loose for a couple of months, then we would have worn it, gotten used to it and been proud of it."
Sir John's Government spent $26 million on a referendum on the subject of changing the flag, conducted over two votes in 2015 and 2016.
The eventual result is that the flag did not change, with 56 percent of people voting to keep the current flag.
Opponents of the referendum criticised its cost and the way it was laid out. Many were upset by the order of questions, which first asked what flag people liked, and once a winner was decided if the country wanted to change the flag to the new one.
Sir John still believes the flag needs an update, more than three years after the final votes were cast.
"I still believe that, as a small country at the bottom of the world if we want people to know us, we need a symbol that is ours," he told 66 Magazine.
There has been no more work on changing the flag since the referendum. Former Labour leader Andrew Little said shortly after the referendum results were revealed the flag could be changed once Queen Elizabeth II's reign ends.
"At the end of the reign of the current monarch I think will be a good time to debate our constitutional arrangements," he told RNZ on March 26, 2016.
"Do we still want our head of state living in London or do we want to do something else and stand on our own two feet? And if we want to do that - then let's have a flag that represents that."