Mackenzie is seeking to understand how all this explosive male energy can co-exist under such brutal conditions, and the answer is with great difficulty.

What makes Starred Up such a riveting experience is that, despite the often unintelligible brogues in which its characters speak, the film so vividly depicts the cutthroat culture of prison life that nothing gets lost in translation.

Director David Mackenzie has empathy for the characters, but also knows how to ratchet up the tension and make the scene of mayhem pack a wallop.

Filmed on a shoestring budget in one of Belfast’s disused penitentiaries, this is a raw, claustrophobic and, importantly, glamour-free depiction of institutionalization.