'Donkey Punch' - the term will be a familiar one to 'Nuts' magazine readers and those given to hanging around the back of bike sheds.

A sexual slang term for what amounts to nothing more than an urban legend, to 'donkey punch' someone is to hit them on the back of the head or neck in order to increase pleasure whilst engaged in a sexual act.

Like any urban legend however, the term has straddled the line of truth and fiction. It is this - the precarious nature of believing in and then carrying out such an act - which is explored in director Oliver Blackburn's tense and well-executed British thriller.

Three impressionable working-class girls from Leeds arrive in Marbella for a girlie weekend, determined to help one of their group get over a break-up back home. Hitting the resorts clubs they soon garner the attention of a group of like-minded British public school boys who impress them by nicking a bottle of champagne and inviting them to board the luxury yacht they're crewing for the weekend.

Sailing the boat out on to the sea, they stage a party which begins with music and copious amounts of drink and drugs, and descends into an all-out orgy. Having spoken earlier about various sex acts and positions, one of the younger teenage boys takes the notion of the donkey punch at face value, killing one of the girl's mid-intercourse.

As the remaining two girls beg to be brought back to shore, the reality of the situation takes hold and the boys begin to realise the possible consequences of what has happened.

Though an accident of sorts, they potentially have an awful lot to lose and so all on board begin to enter survival mode, with factions developing and friendships melting.

With no slasher lurking on board the ship or the usual horror movie clichés, 'Donkey Punch' benefits from a strong, believable storyline, and moves at a credible pace.

Director Blackburn, whose music video background means lots of stylish, sexy shots, constantly throws questions at the audience. As the situation for those on board worsens, we're asked again and again: what would you do? The tension stems from the gravity of the situation and in how Blackburn portrays the psychological horror that is dealing with the aftermath of an accidental death.

That's not to say that the movie is all mind games and doesn't have its gory moments. Various characters meet their demise in a number of horrific ways, yet Blackburn always pans back to the group and to how each death affects them. This mixture of gore and mind games helps ground the story in reality, especially when it threatens to nest in the unbelievable.

A cast made of mainly little-known beautiful Brits helps build the tension. With no actor carrying any baggage into the film, no character's believability is threatened. The lack of established names also means that you're never quite sure who will be killed off next.

Well acted and with a storyline that keeps you on the edge of your seat, 'Donkey Punch' is rarely gratuitous in its sex and violence, and could be placed comfortably alongside 'Dead Man's Shoes' and 'Shallow Grave' as one of the better horror/thrillers in British cinema.

Steve Cummins