Camelot, Channel 4

The story so far: Arthur, an insipid blond wimp (Jamie Campbell Bower), spends his time bonking the local wenches, until Merlin (Joseph Fiennes) drops in one day and tells him he's the heir of Uther Pendragon (deceased) and is now King of Britain. Arthur is baffled but decides to humour the enigmatic wizard, and is soon ensconced in a crumbling Roman ruin on a clifftop, known as Camelot.

He doesn't realise that it's all down to his half-sister Morgan (Eva Green, pictured below) that he's been given this opportunity. She, spurned by her dad Uther, petulantly poisoned him and planned to seize his crown, abetted by boorish and bearded King Lot (the ubiquitous James Purefoy), from Scotland. News of Arthur's rival claim to the throne, and indeed of his very existence, comes as a rude shock to them, and soon they're going to war.

The glory of the Arthurian legends for dramatists and adapters is that there are so many versions of them from various periods and places - take your pick from Geoffrey of Monmouth, Chrétien de Troyes, Alfred Lord Tennyson, Monty Python and many more - that you're free to do whatever you like with them. However, the major liberties taken here are to throw in dollops of gratuitous sex - not least a rumbustious bout between Morgan and Lot to celebrate their unholy power-sharing union - and to make Merlin a skinhead, rather than the habitual King Lear-like figure with Robert Plant's hair and a magic wand.

So far, special effects have been kept to a minimum, leaving aside a few digitally enhanced ruins, though Morgan's shape-shifting scene from young girl back to her adult self was effectively rendered. Otherwise we were merely tantalised by what may lie in store, as Morgan kept vanishing into the depths of the forest by night to practise spells and, flinging off her robe to expose her bosom to the moonlight, to conduct a dialogue with a bad-tempered black wolf (Merlin warned her not to go there, but would she listen?).

Ms Green is rather splendid as Morgan, exuding fanatical ambition and pulsing megawatts of sexuality through fierce, fiery eyes and easily convincing you that mere death won't be enough to curb her lust for power. Purefoy's Lot was good value for these two opening episodes too, as he swaggered about murdering people, guffawing villainously and planning to slaughter everyone standing between himself and the throne, but idiotically, they've already bumped him off.

Fiennes's Merlin may be an acquired taste. He's playing the role as equal parts Time Lord and political king-maker, roving backwards and forwards through time fixing stuff (like sticking Excalibur, "The Sword of the Gods", in a cliff face several centuries earlier so Arthur could pull it out at an opportune moment), and occasionally murmuring ominously about "the darkness of man" or telling Artie that "we're in a fight for the soul of this country". Maybe he's saving his best magic tricks for later in the series.

Nobody else registers at all. King Arthur seems to have surrounded himself with extras from a low-budget surfing movie, including Tamsin Egerton's giggly, blonde Guinevere (pictured above with Jamie Campbell Bower), though there's plenty of slo-mo, soft focus, portentous music and heavily filtered landscape shots to impart epicness and historic significance. But in its bird-brained way, at least it's more fun than that diabolical King Arthur movie with Clive Owen and Keira Knightley from 2004.

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