The last time Derbyshire-born hard man Jason Statham shed a tear on camera, he was probably recoiling from a swift kick to his expendables in one of the testosterone-fuelled action thrillers that have become his trademark.

Big guys, who single-handedly take down criminal fraternities and enjoy gratuitous sex scenes with gymnastic women, don't cry.

Not in public anyway.

So it's a revelation to find Statham laying himself emotionally bare in Hummingbird, a gritty portrait of life in present day London, which suggests there might be a decent actor behind the muscular physique and stubbled chin. Admittedly, Steven Knight's feature directorial debut doesn't test his mettle too strenuously and the narrative is punctuated with bone-crunching skirmishes. However, the fisticuffs are passing interludes, necessary to demonstrate the tortured central character's inglorious past as a soldier, for whom killing was once as easy as taking a breath.

Echoing the grim mood of his scripts for Dirty Pretty Things and Eastern Promises, Knight once again paints the capital as a grimy melting pot of wasted lives and exploitation rather than a gleaming metropolis of neon-lit skyscrapers and opportunity.

On rain-sodden streets, Joey Jones (Statham) sleeps rough with his friend Isabel (Victoria Bewick), hoping to forget about the military court martial that hangs over his head after a blood-soaked tour of duty. The couple are attacked by two thugs and Joey escapes by tumbling through the skylight of a luxury apartment, which is thankfully vacant while the owner is away on business in New York. So Joey uses the flat as a base of operations to get his life back in order by securing work as a bodyguard to underworld figure Mr Choy (Benedict Wong).

Gradually, Joey rediscovers his self-confidence and uses his earnings to buy food for the homeless station run by Sister Cristina (Agata Buzek). However, when Isabel's lifeless body is dragged from the river Thames, Joey's thirst for pain returns and he vows to punish her killer.

Hummingbird is a surprisingly tender account of a war veteran's journey back from the brink of self-annihilation, underscored by a touching romance between Joey and Cristina. The nun's crisis of faith isn't fully explored in Knight's script, nor is the estrangement of Joey from his partner (Vicky McClure) and young daughter, but these heartaches provide Statham with an opportunity to show flickers of his vulnerable side.

Violence is graphic but used sparingly, and at least one growling aside ("You tell me what happened to her or I'll kill you with this spoon!") elicits snorts of derision.

If Hummingbird marks a serious change of direction for Statham, it's very welcome, but with Fast & Furious 7 and The Expendables 3 already in his diary for 2014, it's unlikely he'll be going soft again any time soon.