The federal government has good reason not to release draft laws for an Indigenous voice before a referendum is held, an expert says.

Opposition Leader Peter Dutton has written to Prime Minister Anthony Albanese urging him to release the details of legislation which would set up an Indigenous advisory body, which Labor plans to put to a national vote to change the constitution later this year.

Constitutional lawyer Anne Twomey said the point of the referendum was to put the voice into the constitution, ahead of the parliamentary process to flesh out the details.

“There would be real problems if you did it in advance and gave (voters) the bill and said ‘This is what’s going to happen’ and that people would think that that is what they’re voting on,” she told ABC TV on Thursday.

“When, in fact, the process involves getting parliament to decide those things in the future and change them from time to time where needed.”

She said it was important to have flexibility in terms of how the voice functions, which is why the constitutional change itself needed to be straightforward.

“We don’t want things frozen into the constitution that might be hard to change in the future,” she said.

“We want to have flexibility, so if the voice isn’t working well, if there are problems in it, say corruption or some sort of other issue, then you can legislate to resolve that.”

She gave the example of the 1946 referendum to allow unemployment benefits and other welfare payments.

“You couldn’t say then … ‘Well, we’re not going to allow unemployment benefits unless you can tell us exactly the detail. Who is going to get the benefit? How much it’s going to cost? And how that’s going to work for the next hundred years’,” she said.

The federal Nationals have decided as a party room to oppose the voice referendum, while the Liberals are weighing up whether or not to allow a conscience vote among MPs.

– AAP