At a time when national childhood heroes are being unmasked for wrongdoings in their past, along comes another damming indictment of a well-loved man in the BBC/HBO drama based on the relationship between director Alfred Hitchcock and his twice leading-lady, Tippi Hedren.

Whilst not news to some (Donald Spoto’s book has already revealed a troubled and troubling man), for many this will come as a real shock and, indeed, its recent screening at the BFI upset some Hitchcock aficionados with its deeply unpleasant content.

It is true to say that Alfred Hitchcock does not come out of this ninety minute film smelling of roses. In fact, he smells of desperation and reeks of cruelty. But more of this later.

The story is simple enough, on the surface. An elderly director (Hitchcock, played by Toby Jones) falls for his new leading lady (Hedren, played by Sienna Miller) – hardly earth-shattering. The master of suspense hires her, after a prod from his wife (Alma, played by Imelda Staunton), for his new film, The Birds.

At first, their relationship is fun, with Hitchcock coaching superbly and sending her potatoes (so she won’t get too slim) but it’s not long before Hitch starts acting like a creepy teenager, subjecting his muse to disgusting limericks and a distressing lunge in the back of a car.

From hereon in, The Girl plays like a Hitchcock film, the audience is left unsettled and wondering what the ageing filmmaker will do next to the blonde actress. And what he does is nothing short of a brutal attack as he films the famous scene from The Birds where she is attacked in a telephone box.

It’s a superbly realised and incredibly dynamic moment, captured wonderfully by director Julian Jarrold (Appropriate Adult, Becoming Jane), leaving the actress slightly scarred by broken glass and shocked. But it’s nothing compared to what’s to come.

Hitchcock springs the surprise of filming with real birds, where she was promised fake, as they attack her in another confined space. The director subjects her to countless retakes, resulting in severe trauma whilst her doctor orders rest. Again, a striking and affecting scene that will live long in your memory.

The Girl rather peaks here, and was gripping up until this point. Dramatically the last third can’t live up to its opening as we have too many questions as to why Hitchcock did what he did and why Tippi continued to take it. The director’s motivation is absent, as this is her story, and so Hitch comes off as one his own villains.

Which is fine for fiction but given this film is “based on extensive research”, it does seem rather one-sided. The absence of explanation behind his love for her, and despicable actions, disconnects the viewer from the reality and it’s simply not addressed. Why does he love her? And why does he see her as a “volcano waiting to go off” – we never see evidence of this.

The cast are generally excellent with Toby Jones a perfect choice and flips from limerick spouting fat man to a sleazy sex pest with great skill. Imelda Staunton, as his wife Alma, too is superb; she contains her rage succinctly and her involvement in the cruelty is implicit. Miller plays Tippi like her onscreen persona; this is very much a performance and matches the luscious visuals throughout.

On the eye, it’s an absolute treat. A technicolour treat that looks like it’s stepped right out of the Sixties. Thus giving it an unreal and dreamy feel at times. Despite the warmth of the direction, The Girl is a rather cold and sterile watch, ironic given its passion and dramatic events. Visually, it’s a perfect suit for the events but the audience may well be left wondering just why Hitch was so odious to Tippi.

It’s summed up perfectly in a conversation between the two; regarding her character, she asks him, “Why does she go up on her own?” Hitchcock replies, “Because I want her to.” An answer, not an explanation.

Airs at 9pm on Wednesday 26 December 2012 on BBC Two.