It is one of the most controversial novels of the past decade, a haunting best-seller that prompted discussion about motherhood and troubled children and probed the traumatic subject of high school massacres.

Now Lionel Shriver's We Need to Talk About Kevin, which has sold more than 600,000 copies in the UK, is to be the next film by Scottish director Lynne Ramsay.

However, while Ramsay, award-winning creator of films such as Ratcatcher and Morvern Callar, toils on a lengthy adaptation of the novel, Shriver is becoming increasingly anxious about the film.

The writer, speaking to The Herald from her home in New York, said she has had no contact with Ramsay for more than two years about the movie, which is to be produced by BBC Films.

We Need to Talk About Kevin is a dramatic choice for Ramsay's third film. It follows the agonising emotional journey taken by the mother of a boy who commits an appalling high school massacre.

The novel also sparked debates about the nature of motherhood and maternal ambivalence.

However, Shriver, who won the 2005 Orange Prize for the book, wants to do some talking of her own - with the film-makers.

"There has been no phone call or e-mail in years, no get-togethers," she said. "Yes, I am a little frustrated. But I do not understand much of the movie world, and I accept there are particular challenges in writing a movie script."

She added: "I understand it is a big project for her. It is a book that has sold thousands of copies in the UK alone, I am supportive of that and appreciate that she wants to do the best job she can."

Shriver, currently based in New York, admitted she was "exasperated" by the lengthy process of bringing the novel to the screen. She said after early promises that she would be involved in the film, she has not heard from Ramsay.

The only hint she has had that the movie is ongoing is that BBC Films extended the right they have to film the novel earlier this year.

Other aspects of the adaptation also concern the author.

It has been rumoured that Ramsay is to alter the chronology of the book, which informs readers of the school massacre from the start, but slowly reveals other disturbing details as the plot proceeds.

Shriver strongly believes that if the movie uses a more linear plot, beginning with Kevin's childhood and ending in the massacre, a powerful aspect of the novel will have been lost.

"I think that's a bad idea and I don't mind saying so," she said. "The plot proceeds with not all the facts shown. But I withheld those facts for a reason: it would have been a big mistake, I thought, to have tried to write it as though the school massacre at the end was a big surprise."

Shriver is complimentary about Ramsay's previous work, which is known for its lyrical visual imagery.

"I have seen Ratcatcher and I thought it was arresting, visually striking and she has a great sense of light. Morvern Callar was a little less interesting," she said.

A spokesman for BBC Films said: "We're currently waiting for a new draft of the script."

A spokesman for Ramsay confirmed she was still working on the script and it has not yet been submitted to the film's producers.