By Nigel Powlson

POLITICIANS already put under pressure by the Chilcot inquiry will be casting a wary eye towards Paul Greengrass's incendiary thriller Green Zone.

Greengrass has already given us one war on terror movie, the September 11 hijacking drama United 93, but here he delves into the more murky waters of the political motivations for the invasion of Iraq.

The Green Zone in question is the occupied part of Baghdad, where American forces have set up a political and military HQ and are attempting to run the country after deposing Saddam.

Wily Defense Intelligence agent Clark Poundstone (Greg Kinnear) has the job of legitimising the invasion and dispatches Chief Warrant Officer Roy Miller (Matt Damon) on a series of dangerous missions in search of the weapons of mass destruction that were supposed to be a major threat to western security and safety.

But Miller's men come up empty-handed and begin to believe they are on a series of manufactured wild goose chases.

That suspicion is compounded by a probing journalist (Amy Ryan) who is looking to Miller for answers and a CIA agent (Brendan Gleeson) who wants to recruit the soldier for his own ends.

With Miller tempted off Poundstone's agenda, he brings in a special forces operative (Jason Isaacs) to act as a thuggish counterweight.

Green Zone is first and foremost a thriller and as it reunites the director and star of the last two Jason Bourne films, it's bound to be compared with that franchise.

Certainly in terms of intensity and quality those comparisons are legitimate but thematically this is closer to Body of Lies or The Hurt Locker without aping either of those films.

But as you would expect from a director who spent years dropping into war zones for ITV, Greengrass isn't content just to use a conflict to generate thrills. There's plenty of bite here for those looking to explore the politics.

The need for the US administration in particular to save face and justify its posturing; the shifting sands of what the invasion was actually about; and the culpability of the press in wrongly shaping public opinion are all explored.

Damon has proved the perfect cypher for Greengrass in the Bourne movies and here again fits effortlessly into the central role. Everyone else plays to type to keep the story ticking in the right direction.

It's more ambitious than The Hurt Locker's grunts on the ground eye view and therefore lacks the focus of Kathyrn Bigelow's film. And at times you feel that there had to be compromises to ensure a film with a big budget still had the power to please the popcorn crowd.

But Greengrass has proved yet again that you can make a compelling mainstream film and still explore morally complex issues that genuinely matter.

GREEN ZONE

CERTIFICATE: 15

RUNNING TIME: 112 mins

STARTS: Today at the Showcase, Odeon and Cinema De Lux in Derby and Cineworld in Burton.

RATING: 4/5