Support for same-sex marriage has taken a dive in the latest opinion polling, but campaign experts say this could actually help the final ‘Yes’ vote by reducing complacency among those who want to see change.

Marriage equality supporters make up 57 per cent of voters, down from 63 per cent in August and 62 per cent in September last year.

The ‘No’ vote has lifted to 34 per cent, from 30 per cent in August and 32 per cent a year ago.

The Newspoll results, published in The Australian on Monday showed nine per cent of voters are uncommitted.

Commentator and advertising expert Jane Caro said some backlash would help mobilise ‘Yes’ voters.

“A lift in support for ‘No’ is probably just what the ‘Yes’ side want. It helps undermine complacency and energises their supporters,” Ms Caro told The New Daily.

“For the ‘Yes’ case, this campaign is not about changing hearts and minds – they’ve done that already.

“It is about making sure that those who support them are not complacent about a win and make the effort to fill in their form and post it.

“They don’t want a Trump or Brexit result where lack of voter turnout really made the difference.”

The ‘Yes’ campaign was criticised on Saturday after sending out text messages to thousands of Australians using random computer-generated phone numbers.

“The Marriage Equality Survey forms have arrived! Help make history and vote YES for a fairer Australia,” the text said. Photo: Supplied

While the ‘Yes’ campaign was trying to ensure a high voter turnout, Ms Caro said the ‘No’ group was tasked with changing minds.

“They know they can’t do that directly, so they are using generalised fear and uncertainty,” she said.

“It is a textbook right wing play, used fairly successfully about climate change and abortion rights and euthanasia.

“It is unsurprising therefore that they are experiencing a small lift in support. Their tactics are biting.”

Dee Madigan, Creative Director at campaigning consultancy Campaign Edge, said the automated text would “annoy” voters.

“I honestly don’t think it would necessarily change votes, but it’s resources that are diverted from somewhere else that might get votes,” Ms Madigan told The New Daily.

“When they’re outspent by the ‘No’ vote campaign, that’s a stupid tactic.”

She said the text shouldn’t have been sent out to a randomly generated list, and said it could have been more amicably worded purely to remind people to hand in their vote.

The campaigns prepare for run to the finish line

A spokesman from the Equality Campaign said the advocacy group did not take polls for granted.

“We’ve never been complacent in relation to the national survey,” the spokesman said.

“It’s really important that we reach as many people across Australia as possible.

He said the ‘Yes’ camp had run an “incredibly positive campaign, that’s simply about a fair go for every Australian”.

“We ask every for Australian to be equal under the law, and that’s a beautiful thing,” he added.

A spokeswoman from the Coalition for Marriage said the ‘Yes’ campaign had been “arrogant and out of touch”.

“The campaign is a divided chaotic collection of activists and extremists who don’t seem to have any feel for Main Street Australia and our values,” she said.

“Our efforts moving forward will focus on engaging with every voter possible and encouraging them to vote and to vote no.”