A leaked script for Benedict Cumberbatch's upcoming WikiLeaks movie The Fifth Estate has been posted on the whistleblowing website weeks before the movie is due to hit cinemas.

The British actor plays WikiLeaks founder Julian Assange in the new film, which tells the story of the Australian journalist and his controversial website, and it recently premiered at the Toronto International Film Festival in Canada.

However, the film's script has now emerged online weeks before the film's official release in October (13). It has been posted on WikiLeaks.org with a message from the website's editors, who call the movie "irresponsible, counterproductive and harmful".

The note reveals the film script is a "mature version, obtained at a late stage during the principal photography of 2013" and goes on to defend the site against accusations made in the story.

An extract reads, "The film is fictional. Most of the events depicted never happened, or the people shown were not involved in them. It has real names, real places, and looks like it is covering real events, but it is still a dramatic and cinematic work, and it invents or shapes the facts to fit its narrative goals... People should not in any way treat this film as an historical account of WikiLeaks, its activities or its personnel. Hopefully, they will be inspired to approach the topic with an open mind, and to support WikiLeaks... Although The Fifth Estate purports to be about Julian Assange and WikiLeaks, the film was made without the involvement of WikiLeaks or any of its staff, including Julian Assange."

Assange has previously criticised the film and even wrote an email to its star, Cumberbatch, urging him to walk away from the lead role.