Antoine Fuqua's King Arthur is the story of Artorius, a half-Roman, half-British soldier appointed to defend one of the last outposts of Marcus Aurelius' empire at Hadrian's Wall. He is backed by a rabble of so-called knights, who are Russian conscripts striving for nothing more lofty than their discharge papers. As Arthur is torn between his love of an idealised Rome and his commitment to needy Britain, it is left to a scheming Guinevere (Keira Knightley) and an un-magical Merlin to persuade him to do the right thing.

Billed as the "definitive version" on the basis of historical research that supported the screenplay, King Arthur promised blood, guts and gritty realism, but that translates to a few splats of strategically placed mud, lots of fire-throwing and some exceptionally scraggy beards (it is entirely laudable that Ikea attempted to ban them).

In an attempt to emphasise the film's integrity, the action is dotted with virtual signposts that imply the audience isn't quite clever enough to work out the intended tone for itself. In the knights' first scene, Bors (Ray Winstone) cracks a bad joke about urinating. The sign says: "look how rough and crude these men are, there's no chivalry in this reality".

The billows of superfluous smoke that appear behind Arthur at key moments are an even less subtle way to inform viewers that their hero (Clive Owen) is "smouldering" - just in case his acting fails to get the message across. Put a Guy on a bonfire and you'd get a greater range of facial expression.

The most captivating force is easily Ioan Gruffudd as the seething, damaged Lancelot. He and a composed Guinevere share some of the film's finest moments. "You must be scared," he comments, as they line up their bows to face a horde of Saxons on a frozen lake. "Don't worry, I won't let them rape you," she replies, as cool as the ice cracking beneath their feet.

It's a pity more wasn't made of the spark between this pair, but despite repeated allusions to the fact he is a bit of a cad, this Lancelot is so loyal he'd rather be skewered than meddle with his best mate's bird. His attitude would be a welcome antidote to the post-Beckham exposé era, if it wasn't so hard to credit that a man of Lancelot's mettle would be dedicated to a plank like Arthur.

In a conclusion, mirroring the end of this summer's other blockbuster disappointment, Troy, a Lancelot voiceover entreats viewers not to mourn the dead knights, as their deeds will remain in the nation's memory forever. In my memory, these particular knights' deeds will be lucky to last until next week.