Saving Mr Banks, the story behind the making of Disney's Mary Poppins, is in cinemas now. Laura Delaney finds out if it's practically perfect in every way and talks to one of the film's stars, Colin Farrell.

Outwardly, Saving Mr Banks tells the magical tale of a singing nanny with a flying umbrella who likes to eat spoonfuls of sugar. But when you read between the lines, this movie bookmarks pages of darkness and heartache in a story that has been longing to be told.

The movie details how Walt Disney (Tom Hanks) attempts to charm author PL Travers (Emma Thompson) into signing over the rights to her precious Mary Poppins character. After 20 years of persevering, Walt finally convinces the financially-strapped scribe to take an all-expenses-paid trip from London to the bright lights of Hollywood.  

Even with the promise of script approval, Travers is reluctant to sign off out of fear that Walt and his team - consisting of music and lyricists Richard (Jason Schwartzman) and Rob Sherman (BJ Novak) and screenwriter Don DaGradi (Bradley Whitford) - will make her creation too animated and sparkly.

Meanwhile, flashbacks to PL's chaotic childhood (played by outstanding newcomer Annie Buckley) in Australia with her loving but troubled father (Colin Farrell) and mother (Ruth Wilson) gradually reveal why she is unwilling to give up her beloved book without a fight.

Thompson is sublime as Travers, a petulant, plain-speaking woman, who has no time for small talk or soppy stories (not to mention dancing penguins). An audio recording of the real Travers that floats over the end credits shows how exact her performance is.

Underneath her tightly permed hair and cynical persona is a deeply misunderstood woman who struggles to battle with the ghosts of her past. Thompson brings viewers on her emotional journey with the utmost care and sensitivity. The moment when Travers sees the finished film in all its glory creates a really special and rewarding scene. It looks like Oscar number three may be on its way to Thompson.

Hanks is equally mesmerising as Disney, a likeable guy that remains a shrewd businessman underneath it all. His diplomatic approach to dealing with Travers provides some comedy gold moments. However, it's his final speech about the power of storytelling that really steals the show.

Farrell conveys both the appeal and failings needed to create the emotionally powerful backdrop of Travers' traumatic childhood. There is also terrific support from Paul Giamatti, who plays Travers' assigned driver, Ralph. Kelly Marcel and Sue Smith's script is genuinely moving and is backed up by a delightful score by Thomas Newman. Supercalifragilisticexpialidocious has never sounded so good.

The flashback scenes are enjoyable but just a tad too long. The real payoff comes from the intricate period detail in the early 1960s setting, from the Disney studios to the magical theme park itself.

The mixture of heart and honesty makes this bittersweet film go down in the most delightful way.