Organisers of the Man Booker prize have announced the biggest rule-change in its 45-year history with the confirmation that all English-language writers will be eligible from next year.

That means American writers such as Marilynne Robinson, Jonathan Franzen and Richard Ford can now be contenders for an award that has been restricted to citizens of the Commonwealth (including Zimbabwe) and the Republic of Ireland.

The prize trustees said they had consulted extensively – talking to 40 or 50 writers, readers, booksellers, publishers and agents – for 18 months before deciding on the change.

Jonathan Taylor, chairman of the trustees, said they had first thought about setting up a separate prize but were wary of jeopardising or diluting the existing one. Expansion, he said, was about reinforcing the prize's standing as the most important literary award in the English-speaking world.

"We are embracing the freedom of English in its versatility, its vigour, its vitality and its glory wherever it may be. We are abandoning the constraints of geography and national boundaries."

His fellow trustee Helena Kennedy said there were people writing novels in English in places such as China, Brazil and Israel and it was wrong that there was a kind of "border control" preventing writers from competing depending on what passport they carried.

The prize's director, Ion Trewin, said trustees had been concerned about increasing the number of books judges have to read. This year it was 151.

For that reason they will change the eligibility rules. Instead of publishers being able to submit two books it will now depend on how well they have fared in the competition previously. Publishers who have had five or more longlistings in the previous five years will be able to submit four books but that will go down to one book for a publisher with no longlistings.

For that reason they will next year change the eligibility rules. Instead of publishers being able to submit two books, it will now depend on how well they have fared in the competition previously. Publishers who have had five or more longlistings in the previous five years will be able to submit four titles; those with three or four longlistings can submit three; down to one submission slot for a publisher with no recent longlistings.

The central rule remains that the books must be published in the UK and judges will still be able to call books in that have not been submitted.

Concerns that winning the Booker prize will be far more challenging for UK and Commonwealth writers was a "glass half full, half empty argument" said Trewin, arguing that increased competition would make winning an even greater accolade.

Nevertheless, many writers have expressed disappointment at the change. Philip Hensher writes for the Guardian: "I don't think I've ever heard so many novelists say, as over the last two or three days, 'Well, we might as well just give up, then.' "

The inclusion of all English language writers has been talked about for years but has been resisted, partly because of the problem of different publication dates in the US and UK. It was only two weeks ago that the prize's director, Ion Trewin, told the Bookseller that the trustees were not minded to change the rules.

Taylor admitted organisers had been "bounced into" announcing the change early after it was leaked over the weekend but denied that it had anything to do with the emergence of the new Folio prize.

Andrew Kidd, founder of the Folio prize, said he was in some ways surprised by the announcement.

"We can't help noting that the new criteria are identical to ours but, at the end of the day, there's absolutely no reason that we can't both flourish. I don't see there being any inherent competition between both prizes."

It is something of a game-changer for the award. The academic David Brauner, from the University of Reading's department of English literature, is an expert on US authors. He has looked back on Booker winners from 2000 onwards and believes the only one who would undoubtedly have won if challenged by American competition would have been Hilary Mantel for Wolf Hall in 2009.

He believes Jonathan Franzen's The Corrections may well have triumphed over Peter Carey for True History of the Kelly Gang in 2001 and that Richard Ford's The Lay of the Land might have beaten John Banville's The Sea in 2005.

There will be one big difference in that publishers do not submit books for the Folio prize, with the bulk of the list decided much like the Oscars are decided – by an academy of writers and publishers and editors.