With US election coverage outstripping even the column inches dedicated to our own leadership contests, the UK's appetite for American politics remains insatiable.

It's not a position that's reciprocated, says Stephen Gyllenhaal, director and co-writer of Grassroots, a political comedy loosely retelling the Seattle City Council run-in of 2001. "Sadly the United States is very insular. It's a very divided country. The middle of the country is pretty involved with itself, but there are the coasts which are more progressive and more attuned to the rest of the world."

For armchair analysts with one eye still over the Atlantic, Obama's re-acquaintance with the White House is a fitting backdrop for the UK release of the film on November 9.

Unlikely politician and sometime angry music critic, Grant Cogswell (Joel David Moore), recruits friend and fellow out-of-work scribe, Phil Campbell (Jason Biggs), to spearhead his campaign to bring liberalism - and a monorail - to the good people of the Emerald City.

"I loved the idea of this totally unqualified guy throwing his hat into the ring of politics," says Gyllenhaal. "The idea of this slacker dude going up against the only African-American in the running. One of the great things about grassroots politics is people start at the bottom. The truth was that here were guys that threw themselves into this process for all the wrong reasons, then began to grow up and realise what they have to do to run a campaign."

The glitzy fanfare that punctuates US governance contrasts with the product we ultimately consume. But the film's arch is more relevant than ever, according to its maker. "Romney and Obama rely almost entirely on grassroots politics. You've got the Tea Party on the right wing, and the smaller progressive organisations on the left. It's an illusion that there's a few people at the top level working everything. Really it's people at the local level making everything happen."

The narrative is a reboot of the book written by the real-life Phil Campbell, called Zioncheck for President: A True Story of Idealism and Madness in American Politics. "Not nearly as much of the idealism and madness makes its way to the top as we'd like," Gyllenhaal said. "But the other side of the coin is that running the country is a brutal job. Running for office was a mechanism that replaced war, but at times it doesn't feel all that different."

Grassroots lacks the conviction of its director. Ultimately, it fails to pick at the scab with any vigour, falling between two stalls like the pen of an indecisive voter wavering between red and blue. It's part lightweight politics, part heavyweight bromance, suffering from an identity crisis that political analysts would concur is an irreconcilable position. Moore and Biggs have a compelling on-screen chemistry, but too often there's the expectation that kooky goofball Seth Rogen will pop up from behind a couch or a rostrum (he doesn't). "Like any romance there is a synergy that moved the story forward, but making a movie there are rough spots," admits Gyllenhaal. "It's a process of testing whether it works or not, but I think the two characters parallel each other."

Cedric the Entertainer (as Cogswell's opponent Richard McIver) and Christopher McDonald add weight to the knockabout cast, but it's not enough to elevate Moore's hyperactive delivery. In spite of the character's shortcomings, the staunchly liberal director (father of actors Jake and Maggie), would have voted for Cogswell. "I would have, but with some reservation. Despite the fact that he lacked the political abilities and the experience of McIver – and I also liked McIver – ultimately Cogswell would have done the better job."

The counterpoint to local administrations' spin and smear is bureaucracy and boredom. So it's no surprise that Gyllenhaal aims his focus at the more beguiling aspects of the true-ish interpretation. "The ending is what actually happened," he explains, "but of course we changed things a lot. We were taking a piece of non-fiction which had many, many stories, and making it into what is essentially a short story. There are always people surrounding you when you make movies, investors and various other people. There were some things that they felt should be out of the movie – 9/11 for example - but I was adamant that it was important to the picture, and it stayed, but it changed a lot of things."

In compromising, Gyllenhaal arguably consigns Grassroots to the status of an also-ran that voters neither love nor hate. Its strength is the insight into the struggles and stonewalls that the Obamas of this world faced at the dawn of their careers. The college idealism the director attempts to parody comes over as sincere, peppering the early narrative with clunky frat party banter, while knowing swipes take chunks out of other totems. In one exchange, the movie says more about the pompous, self-aggrandising world of the journo than it manages in 90 minutes about policy. "I'm a journalist - people respect that," Grant opines, before Phil shoots back: "You're an unemployed music critic – people know the difference."

It's frustrating that Gyllenhaal's articulate political nous fails to penetrate the acetate, as the passion of his conversational bluster is disarming, given the watered-down final cut. "I think almost anyone in the United States could be a President. I look at the way the world is run right now by the elite: global warming, wars, the rich having too much. Doesn't it make sense that there are better people out there who could run the country better? That's ultimately why I made the movie, to explore that concept."

In truth, the concept could have been explored further, given the director's sharp political instincts. "What's happened in the Middle East and what's happened in the UK over the last 30 years has been very interesting and to some degree has mirrored the United States," he notes. "I'm voting Obama. I'm hoping that the grassroots movement in this country gives him more progressive support in getting out of the wars, more support for women, healthcare being finalised, education at an affordable price, and that Wall Street's reined in and the wealthy have to pay more taxes."

Grassroots goes on nationwide theatrical release from Friday November 9.