I've seen this twice, and I'd say that IMDb underrates it at 5.9. At 82 minutes, it's lean. It's low-budget, involving few characters and quite a lot of countryside exteriors. Roth is excellent as a low-key hitman. Mullan is extraordinary in his rage. O'Connell handles his young adult role winningly. The femme fatale angle is not as prominent as the review implies. The movie's core is Roth and O'Connell, with start and finish bringing in Mullan.
Here's an accurate review by Derek Winnert.
The Liability *** (2012, Jack O’Connell, Tim Roth, Peter Mullan) – Movie Review
Jack O’Connell shows why he’s a rising star in a compelling performance as 19-year-old Adam, who’s forced to do a day’s driving for his mum’s gangster boyfriend Peter (Peter Mullan).
This leads the boy on a madcap tour of the wild side through murder, sex trafficking and revenge, guided by hired assassin Roy (Tim Roth).
A femme fatale (Talulah Riley) soon hoves up at a critical moment, turning the yarn into a three-way game of cat and mouse. Thrilling violent moments mix with funny wry humour in a satisfyingly oddball thriller, with a nifty script and four good actors to make it work. Excellent though veterans Roth and Mullan are, O’Connell sure gives them a run for their money.
John Wrathall’s inventive script boasts funny dialogue, and it’s nice and dark and well plotted, tense, twisty and involving to the end. The relationship between Roth and O’Connell’s characters is very profitably developed and explored.
Advertised as ‘From the executive producer of Lock Stock and Snatch’, it inhabits a similar dangerous world of unpredictably violent, lazy low lifes.