The former prime minister Tony Abbott may be one of the strongest opponents of same-sex marriage but as the September postal plebiscite approaches, his electorate has revealed it overwhelmingly supports gay marriage.

Almost 700 residents across the federal electorate of Warringah were asked if same-sex couples should be able to get married.

Almost seven in 10 (69.7%) agreed they should, 25.7% did not and 4.6% were undecided.

The poll was conducted by the left-leaning Australia Institute.

Majority support was revealed across all age groups – the 18-34 bracket led the charge with 83.9% in favour.

Even the age group with the lowest support, 65 and older, came in at 57.3% in favour.

Liberal voters polled 60.3% in favour, Labor voters 88% and every Green polled expressed support.

The lowest support came from One Nation voters, of whom 68.3% opposed same-sex marriage and only 22.3% supported it.

“There is a massive mood for change on marriage equality around Australia, and this poll is further evidence of that,” the Australia Institute executive director, Ben Oquist, said.

“Warringah voters look set to overwhelmingly back marriage equality and they do not appear to be buying into the line that the survey has anything to do with free speech or political correctness.

“Time and again polls show the majority of Australians, the majority of Liberal voters back same-sex marriage. This non-binding postal poll is likely to tell the government what everybody already knows,” he said.

– with Australian Associated Press