Outrage and the Man Booker Prize are the equivalent of gin and tonic, and of Christmas and panic-bought book tokens. Less than a week after this year's Man Booker Prize shortlist was announced the murmurs of discontent continued, but not because of the six authors who made the final cut. Last weekend stories began to circulate that, for the first time in its 45-year history, the prestigious prize would be open to American writers.

Until now the award has been open to any full-length novel, written in English, by authors from Ireland, Britain, the Commonwealth and Zimbabwe. Custodians of the prize remained tight-lipped about how the eligibility chips would fall until a big announcement last Wednesday. Not only are American authors now eligible to compete for the £50,000 (€60,000) prize, but so are authors from anywhere else in the world. From 2014 any novel written in English, regardless of the author’s nationality, can be considered. The organisers admitted they had toyed with the idea of setting up a new award specifically for US writers, but they “were wary of jeopardising or diluting the existing Man Booker Prize”.

Initial tutting began about US behemoths such as Cormac McCarthy, Jonathan Franzen and Toni Morrison coming over here and stealing our prizes. Any author from Peru to the Philippines who writes a novel in English is a contender, assuming the book is submitted by its publisher. The new rule immediately bloats the field. So why have the Booker trustees made this decision?

Casting the Booker net wider, and appealing to readers, writers and publishers in different territories, raises the profile of the prize instantly. The Man Booker brand gets global recognition, which may well translate into more sales, but the organisers are also acutely aware that geographical borders are disappearing in the book world. Kindle editions are often pitched globally, and US and UK publication dates, which have varied hugely in the past, have become more synchronised.

The Irish author Anne Enright, who won the Booker in 2007 for The Gathering, believes this new direction is a response to this situation.

“The English-language book market is, like everything else, becoming more international, especially with the rise of the ebook. Also, authors are looking for one single publishing date, so their lives aren’t eaten up by separate book releases and marketing campaigns in Europe and other territories. It is inevitable that a major prize should reflect this globalisation. I always felt the Commonwealth plus Ireland was a bit of a postimperial, sun-setting-over-the- empire kind of categorisation.”

Formidable output
Despite Ireland's formidable literary output, we are a small country, and Irish writers may struggle to get on to future shortlists. Three Irish writers, Colum McCann, Colm Tóibín and Donal Ryan, made the longlist this year. An expansion will mean more nationalities and authors jockeying for the prize. Enright believes homegrown writers will hold their own. "We know Irish writers consistently do well globally, and particularly on either side of the Atlantic, so let's not panic just yet."

A wider field also means more competition, so publishers are more likely to submit their heavy-hitting authors – big names and previous winners – for the prize. This raises a bigger issue: if literary giants become the submission of choice, publishers are less likely to put forward unknown writers or debut novels. As well as new names missing out, future shortlists run the risk of becoming more homogenised, and the same big names will sit cosily alongside each other.

It’s also worth noting that two other high-profile book awards, the Pulitzer and the National Book Award, are open only to US citizens. The Booker will undoubtedly experience some cross-pollination with these lists, which could lead to a less diverse array of nominees.

Smaller publishers and independent presses are also unlikely to be happy with the news. Stefan Tobler runs And Other Stories, an independent subscription press that published Deborah Levy's Swimming Home. After it was rejected by several big publishers, Levy's book made the Man Booker shortlist last year. "It makes sense because it seems as though it wants to be a truly international prize, but it will be harder for smaller publishers," says Tobler. "There is a risk that there won't be enough diversity and that familiar names will dominate. It won't seek out new writers."

Eoin Purcell, commissioning editor at New Island, believes it's a response to the collapsing borders of old publishing territories. "I don't see what writers of quality have to fear from the inclusion of their US peers. In an age of global literature we should aspire to have global literature prizes."

A new literary award, the Folio Prize, will be launched next year. There has been speculation that this prompted the changes at the Booker (whose trustees say the consultation process began in 2011 and predates the new prize). Globalisation for the book industry may end up problematic, with the more financially comfortable players edging out more interesting, diverse voices.

“We have to be suspicious of a monumental approach to literature and marketing,” says Enright. “The best and most interesting work is often niche, and happens at the edges.”