“If beauty is truth, and truth is beauty, then surely mathematics is the most beautiful thing of all?” So says Eddie Marsan’s character, Martin, the International Mathematical Olympiad team leader (perhaps ever so slightly modelled on Bill Oddie) to our young protagonist Nathan, in director Morgan Matthews’ brilliant new film, X+Y. But can you apply a formula to something as abstract and subjective a concept as beauty or truth? Would you even want to? Well perhaps you would, if you’re a young teenage boy coming to terms with the world around you, and above anything else in the world, you really love maths.

Why does Matthews’ film work so incredibly well? Audience members laughed and cried this morning in the press screening at the BFI London Film Festival. And it was a 10am screening on Sunday morning! The first reason: perfect casting. Asa Butterfield as mildly autistic maths prodigy Nathan; Sally Hawkins as his endearing, single-parent mother, and Rafe Spall as Nathan’s maths teacher Humphreys, living with MS and a heavy bout of sarcasm. This trio of actors compliment each other in every scene – striking just the right balance of humour, tragedy, and vulnerability – which leads to a strong urge to empathise with their narrative exploits on screen.

There’s a synchronicity between the musician scoring this film and THE KEEPING ROOM – Martin Phipps. Both scores are packed with engagingly melancholic sequences, but whereas THE KEEPING ROOM was wholly acoustic, with a mixture of violas and harmoniums, X+Y mixes things up with stark strings which shift unexpectedly into euphoric synth motifs, sitting somewhere between Philip Glass and M83. In a particularly moving scene, Nathan walks around the streets of Taiwan for the first time and we see through sweetly spine-tingling visual and auditory stimuli that he is learning to accept and embrace the unknown and different.

Almost every scene is varnished with an invisible lacquer, an underlying sense of sadness…

For a character who finds it difficult to hold the hands of his mother, let alone flirt with a member of the opposite sex, Nathan’s development remains fascinating to watch. Earlier scenes in the film with a younger actor playing Nathan to Spall’s quite wonderfully droll maths teacher Humphreys are a delight to watch. The swearing in these scenes is  naturalistic and harmless, in a manner reminiscent of Chris and Paul Weitz’s ABOUT A BOY. And perhaps this is the closest comparison to draw in the British cinematic output of the last two decades, in terms of successfully balancing a happy and sad tone throughout a feature. Almost every scene is varnished with an invisible lacquer, an underlying sense of sadness, that is somehow overcome in each instance through the character’s drive to persevere and help one another.

There is a great beauty and truth to this film. You don’t need to understand much of the mathematical formulae bandied about in the dialogue. There’s a heartwarming, and at times, heart-wrenching display of the best of this type of British filmmaking on offer. Matthews proves himself a worthy disciple of the Weitz (and perhaps Richard Curtis – in the best possible way) school of filmmaking. Cambridge is depicted in all its spindly towered and greenery-adorned, cobbled side-street glory. X+Y looks set to be just the right sort of film to herald the start of springtime after a meteorologically melancholy winter, upon its release in late March 2015 in the UK.

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