General Peter Cosgrove speaking at a Breakfast at Leonda by the Yarra in Melbourne with local member Josh Frydenberg.  March 25th 2011, THE AGE, Picture by Mal Fairclough

Governor-general-designate General Peter Cosgrove. Photo: Mal Fairclough

Support for an Australian republic has collapsed to a 20-year low, with just 39.4 per cent of Australians saying they support a republic.

Support was lowest among older Australians and Generation Y voters, with people aged 35 to 65 most supportive of abandoning the monarchy.

An exclusive ReachTEL poll of more than 2100 Australians, conducted on Thursday night for Fairfax, shows 41.6 per cent oppose the country becoming a republic; 19 per cent had no opinion on the issue.

Poll conducted by phone, 6–7.30pm, Thursday January 30, 2014. Sample size: 2,146. Margin of error: +/- 2.1%.

Poll conducted by phone, 6–7.30pm, Thursday January 30, 2014. Sample size: 2,146. Margin of error: +/- 2.1%.

Australians for a Constitutional Monarchy national convener David Flint said the findings were a ''time bomb'' for the republican movement, with support among 18 to 35-year-olds at 35.6 per cent. Only those over 65 had a lower rate of support (30.7 per cent) for a republic.

''That is a time bomb, I believe, for republicans, because you don't have that investment for the future,'' Professor Flint said.

Not only were young people uninterested in a republic, he said, they were favourable to the monarchy partly because of the star power of the ''young royals'', Princes William and Harry and the Duchess of Cambridge, Kate Middleton.

SOURCE: FAIRFAX-REACHTEL POLL.

Source: Fairfax-Reachtell Poll.

But Geoff Gallop, chairman of the Australian Republican Movement, said: ''Polls will come and go, but we've been encouraged by the support we've been getting and our campaign will continue.''

Mr Gallop said higher support for a republic among Generation X and baby boomer voters could be explained by them having participated in the 1999 referendum and remembering the 1975 constitutional crisis.

The poll was conducted less than a week after Prime Minister Tony Abbott named General Peter Cosgrove as governor-general-designate, saying he could ''not think of a better person'' to fill the role than General Cosgrove.

''Throughout his life, he has demonstrated a commitment to our country and a commitment to service. He has given service of the very highest order to our country,'' he said. ''I am confident that in this new role he will continue to deliver to a grateful nation leadership beyond politics.''

General Cosgrove was roundly endorsed by male voters in the ReachTEL poll, with 61.9 per cent of men saying he was a better choice for the role than the present Governor-General, Quentin Bryce.

Five years ago, Ms Bryce became Australia's first female governor-general. She is due to retire in March.

Among women 52.6 per cent supported General Cosgrove and 47.4 per cent preferred Ms Bryce.

More than 70 per cent of respondents over 65 said General Cosgrove was a better appointment and 65 per cent of respondents across all age groups backed his appointment.

That figure is highest among men and older Australians, with a whopping 80.3 per cent of Australians 65 and older approving of his appointment.

In November, Ms Bryce used the final Boyer lecture of the year to publicly support the push for Australia to become a republic.