Sixteen is not a good age for horses. And fifteen is proving equally difficult for Mia. Fifteen going on 50, Mia lives an isolated, disaffected life. A school drop-out, labelled weird and smelly by her peers, she is neglected by her single-parent mother and converses at a bawl with her younger sister, who is 8 going on 40. Mia haunts the high-rise she calls home, sneaking alcohol and ciggies where she can get them. Her only pleasure is dance, which she practices solo in an upstairs derelict flat. Something has to change, and the catalyst proves to be Mum's new boyfriend. Both creepy and charming in the manner of David from An Education, the boyfriend seems to take Mia seriously. Perhaps too seriously.

Fassbender excels as the charismatic interloper. He is always the smartest - and best-looking - guy in the room, without rubbing your nose in it. When he does lose control, we unfortunately cannot view his reaction because he is only seen in silhouette. Having seen him in Hunger and Inglorious Basterds, he clearly has chameleon-like abilities.

The film moves along a tad too slowly, teasing out the will-they-won't-they relationship between Mia and the boyfriend. Once that is resolved the pace becomes frantic, and the consequences that follow are harrowing.

The British underclass seems to be Arnold's setting of choice. I am not convinced she is at home here, or even that she has spent much time amongst the people she loves to represent on screen. Mia's younger sister, especially, seems archetypical - a can of beer in one hand, a ciggie in the other, expletives falling freely from her mouth, she does not seem to be anything other than a Daily Mail reader's portrait of Britain's feral kids. Mia, also, seems to spend 24/7 in a rage. A more tempered view, even a spot of gallows's humour, would make this arena more believable. There is a bit of a sneer here from the writer-director that is distasteful. I am also sceptical about the Katie Jarvis hype - she does well, but there is nothing in the role to suggest a trained actress could not have handled it. Of course, casting a trained actress would not have generated so much press as the fighting-with-her-boyfriend-at-the-platform story....

All that is forgiven, however, for one sequence that is among the most viscerally compelling I have ever seen on screen. It takes place when Mia is at her lowest ebb, and decides on an action that is less than half-thought out. It is completely understandable given all that has gone before, but connotes Jamie Bulger, Soham, and a host of other unspeakable acts from the cultural memory. Shot verite style, raw and unforgiving, the sequence is a masterclass in how to put an audience through an emotional wringer. The building rhythm of a little girl going up and down on a scooter. A ferocious splash in the ocean. An eternity before re-surfacing. Even the memory of it has me sweating from the palms. Brave, sublime filmmaking.

There are other small moments - three generations of women dancing, a horse spied from a road - that suggest a mature, accomplished style is evolving in Arnold. Wasp was well-executed. Red Road I just found incredulous. Fish Tank has subtlety and bombast, not always in the right mix, but courageously attempted. I will come back to Arnold. Hopefully, one day she will turn her scorn on the tax-dodging upper class who are equally Britain's trial and shame.

At first I wasn't sure what to make of this movie. Having watched "Red Road" by Andrea Arnold, I needed to watch Fishtank. It wasn't quite as good as Red Road but somehow it had something that mesmerised me. The movie tells of a 15 year old girl living in a rather socially deprived area of Britain who is passionate about dancing. Her mother is a drunk and brings home a new boyfriend one day.

Right from the start there are scenes that are hard to take. These scenes felt quite real for me, maybe thanks to the Director or the acting. There is not much of a storyline other than that the girl gets involved with her mother's boyfriend and everything gets even worse after that.

I thought that Michael Fassbender's performance was brilliant. He seems to be star in the making.

This movie makes difficult watching because of the harshness of the lives that are depicted here.

Fish Tank hits you deep and hard, in the soul. It drew me in to its world without me hardly noticing it - a world of ultra-realism, burnished, you must say, by some quite incredible performances from Katie Jarvis and the rest of the cast.

One night of disturbed sleep after watching it and I am still in their world, out on the bleak and beautiful flatlands bordering Essex and London which so many people speed through every day as they journey between London and mainland Europe on the Eurostar trains. I myself have taken that journey a few times and wondered what the people's lives were like who lived in this strange landscape where London has parked so much of the stuff that it doesn't want to see - the giant container terminals, the power plants and the chemical works.

Fish Tank perhaps gives a taste of those lives, but it does much more than that. Especially it gives us a heroine who we can't help caring for deeply, despite and partly because she is on the outside so nasty, rude and violent. Through some of the things she gets up to as she wonders around we see a natural love of life bursting to get out though. We also have an attractive and kind man come into the picture who, through his natural goodness, offers an outlet for her yearnings for understanding, fun, and intimacy.

The story starts off slowly as we get to know 15-year old Mia, her family and the wider (and very limited) world around her. But it picks up and becomes tautly gripping at times - and it never slips into sentimentality or offers false redemption. It is all the better for that.