The Australian writer Peter Carey, twice winner of the Booker prize, has criticised the decision to open up the award to Americans for the first time, claiming that the old Commonwealth-only version had a “particular cultural flavour” that would now be lost.

The winner of the 2014 Man Booker prize will be unveiled on Tuesday evening in a glittering ceremony in Guildhall, London. Two American authors have made the shortlist: Karen Joy Fowler for We are All Completely Beside Ourselves and Joshua Ferris with To Rise Again at a Decent Hour.

In an interview with the Guardian, Carey said he was unenthused by the move to expand Britain’s richest literary prize across the Atlantic. Asked if this was a mistake by the organisers, Carey replied: “Let me answer this in a slightly perverse sort of a way. I find it unimaginable that the Pulitzer or the National Book award people in the United States would ever open their prizes to Brits and Australians. They wouldn’t.”

He stressed: “There was and there is a real Commonwealth culture. It’s different. America doesn’t really feel to be a part of that.”

He added: “The old Booker had a particular cultural flavour. The Pulitzer and the National Book awards have their sorts of flavours. I suppose I’m not generally in love with the notion of global marketing.”

Carey’s remarks carry considerable literary weight. He is one of only three novelists to have won the Booker twice, with Oscar and Lucinda in 1988 and True History of the Kelly Gang in 2001; he has been shortlisted on two further occasions. (The other double-Bookers are Hilary Mantel and JM Coetzee). Carey’s nuanced scepticism follows similar top-end grumblings from former winners AS Byatt and Graham Swift, as well as from critics who fear that the decision may see American fiction steamroller delicate new talent from smaller English-speaking nations.

Facebook Twitter Pinterest Peter Carey, pictured in London. Photograph: Sarah Lee/The Guardian

No personal grudges exist among those currently in contention. As well as the Americans, there are three Brits and an Australian. The bookies’ favourite is The Lives of Others by the Indian-born Londoner Neel Mukherjee. Also on the shortlist are Howard Jacobson with J, Ali Smith for How to be Both, and the Tasmanian writer Richard Flanagan, whose The Narrow Road to the Deep North is strongly tipped.

Over the weekend all of the Booker-shortlisted authors appeared at a literary festival in Cheltenham, afterwards chatting companionably in a circle. The conversation ranged through how a Booker nomination multiplies sales (massively); what to do on Tuesday evening if you don’t win (grin a lot); and how the winner needs to brace for a publicity nightmare (the losers go home graciously).

The mood was convivial. The six agreed that any of their books would be a worthy winner. Others who dropped into the marquee-like green room included Rowan Williams and Martin Amis. Afterwards the authors sat round the same table at a dinner hosted by Cheltenham Ladies’ College.

Carey was speaking before the publication next month of his new novel, Amnesia, which is loosely inspired by the story of WikiLeaks and Edward Snowden. The novel, Carey’s 13th, may eventually feature on the 2015 Man Booker shortlist. He said that his misgivings about the revamped Booker were not categorical. “The prize is clearly an ongoing organic thing and we’ll see what happens,” he said on a recent visit to London.

Carey admitted he had not read any of the shortlisted works, other than The Narrow Road to the Deep North, which he hailed as deeply impressive. “Richard Flanagan clearly has to win. He’s our man. He’s a serious guy who can really, really write. I’ve got my fingers crossed for Richard,” he said of his fellow Australian. Flanagan’s novel tells the story of a Australian prisoner-of-war who survives the building of the Burma railway. His luminous narrative deals with the second world war and its aftermath, and with themes of guilt, survival and sorrow. In a Guardian webchat Flanagan revealed that his father – who worked on the infamous “death railway” – died the day he finished the manuscript.

Facebook Twitter Pinterest Carey: ‘There was and there is a real Commonwealth culture. It’s different. America doesn’t really feel to be a part of that.’ Photograph: Sarah Lee/The Guardian

According to Carey, The Narrow Road to the Deep North marks a long-awaited cultural moment. He said that leftwing Australian writers of his generation – he is 71 – were strongly involved in the anti-Vietnam movement and consequently struggled to write fiction about the war and its protagonists, even though they had grown up listening to its myths and stories.

“It’s really extraordinary the degree to which Australian writers of my generation completely ignored all of those Australian soldiers who fought and died. The reason we didn’t want to deal with it was because during the sixties the Returned Services League was generally a very reactionary force and we were the anti-Vietnam movement,” Carey said.

“They were against people with long hair and rock ’n’ roll. Their really justifiable fear and hatred of the Japanese read to us like racism. As a result the literary writers didn’t really want to imagine what those people went through when they died. That’s why [Flanagan’s novel] is really, really important.”

For 45 years the Man Booker prize was only open to authors from the UK and the Commonwealth, plus the republic of Ireland and Zimbabwe.

Last year, justifying the decision to expand it, Jonathan Taylor, chairman of the Booker Prize Foundation, said: “We are embracing the freedom of English in its versatility, in its vigour, in its vitality and in its glory, wherever it may be. We are abandoning the constraints of geography and national boundaries.” The £50,000 prize can now go to any author writing in English for a work published in the UK.

Carey has been recognised by US judges, with Parrot and Oliver in America, which features an imaginary Alexis de Tocqueville, shortlisted for the National Book award in 2010. But this is only because Carey has dual Australian and American citizenship – he has lived in New York since the early 1990s.

Carey said he was disappointed with Barack Obama – for whom he voted in 2008 – and sometimes despaired about the state of American democracy. He also took a swipe at the rightwing government of Australia’s prime minister, Tony Abbott, who has adopted a hardline policy towards boat people and refugees.

Asked whether he voted in Australia, Carey said: “I tried to. I couldn’t. I haven’t had an address in Australia for a long time.” But he said he wouldn’t have voted for Abbott. In joking tones, he said: “Is is true they call him [Abbott] shifty? No, I wouldn’t have voted for shifty.”

Carey also described claims by former prime minister John Howard that asylum seekers had thrown their children into the sea as a “lie of Goebbeleseque proportions”.

He was critical, meanwhile, of the current Australian government’s proposal to bring in a draconian law against whistleblowing. “It’s horrendous”, he said.