It was reported over the weekend that the Man Booker prize will open up to US authors as of 2014, after 45 years of recognising the work of writers from UK, Ireland and Commonwealth countries.

The story prompted concern that the literary award will lose its identity, with writer and broadcaster Melvyn Bragg telling the Sunday Times: "I'm disappointed … though not that surprised. The Booker will now lose its distinctiveness. It's rather like a British company being taken over by some worldwide conglomerate."

In the Independent, Kazuo Ishiguro was quoted as saying he had heard about the change "a few months ago from someone very senior at the prize, and the argument was that the standard hadn't been high enough".

Ion Trewin, literary director of the Man Booker prizes, said on Monday: "There are going to be some changes to the rules of the Man Booker prize for fiction which have been in discussion for some while. The information which is currently in circulation is incomplete." Full details are to be announced on Wednesday.

Author Linda Grant, who was shortlisted for the prize in 2008 for her novel The Clothes on Their Backs said that such a change would "create a huge imbalance"in favour of US authors.

"There are two career-changing prizes, the Booker and the Pulitzer. The Pulitzer has this big market in the US, and UK authors are closed off from that. If the Booker is open to US authors it will create a huge imbalance. UK writers will have more competition for a career-changing prize, whereas US authors will have a new prize."

She continued: "If you publish Richard Ford and Jonathan Franzen, what are the chances that they will not be entered?"

The Booker is currently open to novels by British, Irish and Commonwealth authors published in the UK, with each publishing imprint putting forward two titles, plus titles by previously shortlisted authors. Grant said that for certain writers the requirement to be entered into the Booker is written into their contract with the publisher, and that US agents are likely to be robust in ensuring that this happens.

"The benefit of winning the Booker is overwhelmingly commercial," Grant said. "It's highly unlikely that the book wouldn't be picked up by a US publisher, as well as selling translation rights. The author is much more likely to get a bigger advance for their next book."

The move has been seen in some quarters as a response to the new Folio prize, an award for English-language fiction from around the world published in the UK. With a pot of £40,000, it will be given for the first time next year; a shortlist of eight titles will be announced next February.

Some commentators questioned why the Man Booker would open up to writers from the US, but not elsewhere in the world. In 2004, the Booker Prize Foundation created the Man Booker international prize, worth £60,000; it is given every two years to a writer published in English.

This year's Booker winner will be chosen on 15 October from a shortlist of six books that has been widely heralded as the best in a decade.