Putting a guy in a "box" for the duration of a film isn't a wholly original conceit:

Colin Farrell was pinned down by a sniper in Phone Booth, and Ryan Reynolds spent the duration of Buried in a coffin. But both those films existed in the realm of fantasy; what makes Locke different is that its hero spends 90 minutes in his car - just his car, on the motorway, imprisoned by nothing but his conscience. Locke is an ordinary man, with a common dilemma. Yet, over a mesmerising 90 minutes, this becomes a very special film.

Ivan Locke (Tom Hardy) is a building site foreman, on the eve of the most important day of his career - namely the biggest concrete pour ever in Europe. We can sort of guess what that means; the foundations of a very large building, on which all else rests, literally. But on the night before the pour, Locke leaves the Birmingham site, climbs into his car and heads on to the motorway for London. He settles himself into the journey, and for a series of phone calls that must be completed before he reaches his destination.

All of these calls are fiercely, poignantly practical. First, he must inform his boss Gareth (Ben Daniels) that he's gone AWOL - effectively handing in his resignation - while guiding his extremely nervous right-hand man Donal (Andrew Scott) through the last-minute details that need to be addressed if the pour is not to be a disaster. Then, he must phone his wife Katrina (Ruth Wilson) and tell her why he's driving towards another woman.

It doesn't take us long to understand that, whatever his mistakes, this is a deeply honourable man, caught in the vice-like grip of decency; Locke is intent on doing the right thing, even if that will cost him his family and his career. The poor man has even got a streaming cold, yet navigates the road and his many conversations - including heart-rending ones with his two sons - with a steely will.

Steven Knight is best-known as the screenwriter of the character-driven dramas Dirty Pretty Things and Eastern Promises. This is only his second film as a director - the first was Hummingbird, which featured action star Jason Statham - and so at this point it's difficult to gauge what his distinction may be behind the camera. Nevertheless, Locke really does work, against the odds.

The script is tight, effective and constantly surprisingly, juggling heartrending emotional moments between Locke, his wife and young sons, with the edgily complicated ones with the other woman (Olivia Colman) and the comic absurdity of his exchanges with the hapless (and increasingly drunk) Donal. Even while we laugh, we want the concrete pour to succeed, and somehow his talking Donal through the minutiae of road closures, council permissions and the right setting on a nozzle is lent the edge-of-seat, life-or-death significance of talking a passenger through the controls of an airplane.

Cameraman Haris Zambarloukos imbues the road outside the window with a gorgeous, even mysterious sheen. And despite needing only voices on the other end of the phone, Knight has cast his characters very well. But the focus, for the entirely of the film, is on Hardy. The actor manages to make his middle-class Welshman arrogant yet sympathetic, coolly impressive while teetering on a nervous breakdown as he starts talking to his dead, hated father in the rear-view mirror. The set-up depends on him completely and he delivers with a charismatic, riveting tour de force.