Mary Poppins enchanted me as a child. Full of sumptuous imagery and wondrous melodies, it was one of those family features from Walt Disney that didn't so much tell a story as leave a magical mark on your mind for long after the film was over.

Suffice it to say that Saving Mr Banks, the closing night film of this year's London Film Festival, won't leave the same impression. It's a prosaic picture about the difficult process it took to bring the Mary Poppins book to the screen, starring Emma Thompson as author P. L Travers, Tom Hanks as Walt Disney, and helped down throughout by many spoonfuls of sugar.

Travers is a frosty and frigid middle-aged woman who resides in a picturesque Chelsea terrace house that immediately recalls the Banks family abode from Mary Poppins. We learn that Walt Disney has been harrying her for the film rights the past 20 years, desperate to turn his own children's favourite in to another celebrated product from the House of Mouse.

But Travers' icy fortress repels wave after wave of Walt's charm offensive, as we see her repeatedly turn her nose up 90 degrees to decry the vulgarities of America, musical numbers and most of all "those silly cartoons" upon which the studio has built his empire on.

It's a set-up that grows tiresome excruciatingly quickly. Like all biopics, we know already what is going to happen, meaning that the movie is robbed of any real narrative thrust. You want to bark back at Travers, who seems hell-bent on insulting everyone in her wake, to stop being such a prude so that we can move on to a more interesting stage of the movie.

That never materialises, and we are instead served increasingly contrived flashbacks to her difficult childhood in the Australian outback. Her novel is more personal than most, with many of the book's elements, from the nanny that suddenly appears to the banker father who loses his job, all recollections from her past. These childhood memories of her caring but irresponsible father, the Mr Banks who needed to be saved, are why she is so fiercely protective of Disney commercialising her story.

Emma Thompson is fine as the shrill Travers, the hard abrasive chalk to the big cheese that is Hanks' Walt. The two are complimented by many excellent turns, from Paul Giamatti's kind and friendly driver, to B. J. Novak and Jason Schwartzman humorously playing composers the Sherman brothers. The standout from the bunch is Colin Farrell as Travers' father, using his natural charisma and roguish demeanour to present a man who prefers the fabricated fairytale he spins for his children over the drudgery of everyday life.

Whilst his battle with alcoholism is properly addressed, we're never given a more proving examination of Walt Disney, a heavy smoker who saw a lot of his qualities in Mr Banks and even demanded the character similarly wear a moustache. In a sugarcoated representation he's instead an all-loving figure who helps Travers finally exorcise her demons. That's not really a surprise seeing as the studio financed the picture, but it does mean we're left with a nostalgic feature-length advert to the wonders of Walt Disney. If I needed to be reminded of that, I'd just watch Mary Poppins again.

Saving Mr Banks is screening as part of the 2013 London Film Festival. The film will be released in UK cinemas on 29 November 2013.

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