It is the hot British film of the moment and is even being spoken of as an Oscar contender.
But Martin Sixsmith, who wrote the book on which Philomena is based, appears keen to avoid the limelight: his next project is a 25-part epic series for Radio 4 about the History of Psychology and Psychiatry, RadioTimes.com can reveal.
Whether or not the film, which is released today [Friday], turns him into a star or not, Sixsmith is busy at work on the project which follows his epic History of Russia for the same network. It is due to air in April next year.
Author, presenter and former BBC foreign correspondent Sixsmith studied Russian at university but after losing his job as a government spin-doctor did a psychology degree in 2002.
“I did it when I fell out with Tony Blair or rather Tony Blair fell out with me. I don’t pretend that I am the world’s greatest expert on every aspect of psychology, [but] I do talk to a lot of the experts.”
The 59 year old is due to fly out to America to publicise Philomena which opens there on November 22.
Based on his 2009 book The Lost Child of Philomena Lee it tells the story of his attempts to find the son Philomena Lee was forced to give up by nuns in 1950s Ireland, and who was subsequently adopted by a wealthy American family.
Sixsmith is played by Steve Coogan while Philomena is played by Judi Dench.
In the film, certain real life events have been altered for dramatic licence, Sixsmith explains.
In reality, Sixsmith and the real Philomena never travelled to America together but the film depicts them embarking on a road movie in search of her lost son.
“It didn’t happen like that, I went off on my own to America. It was only me going and Philomena stayed at home in St Albans where she lives. I obviously kept her updated. But for dramatic purposes we had her going with Martin to America.
“It does not bother me. It is clear why they had to do it because the heart of the film is the relationship with Philomena and you can’t do that over a telephone."
Sixsmith says he sees stark differences between his own personality and the character played by Coogan.
“The character changed from me to the character that you see on the screen,” adds Sixsmith. “I hope they exaggerated Martin’s snobbishness”.
He said Coogan's often spiky character in the film is designed to represent the feelings of the audience, especially in scenes where he expresses anger about the way Philomena was treated.
“Martin [gets angry] on her behalf,” he says.
“The way Judi Dench plays her as a power for good, she is like that in real life,” he added.