Directed at full pelt by Matthew Vaughn, Kingsman: The Secret Service is an outrageous James Bond-esque caper with an unpleasant and sadistic streak.

This hare-brained tale about a secret organisation of impeccably tailored British agents dedicated to world peace lampoons the conventions of the spy genre with an arched eyebrow.

"Nowadays, they're all a little serious for my taste," opines Colin Firth's lead operative about modern-day spy films, one of several self-referential winks in Vaughn and Jane Goldman's script.

"Give me a far-fetched plot any day," he quips, and that's just what Kingsman delivers in spades.

Unfortunately, the film also serves up a blitzkrieg of gratuitous on-screen barbarity. The violence doesn't support the plot, the plot is constructed to support as much wanton carnage as Vaughn can cram into each frame.

This stomach-churning slaughter reaches a nauseating crescendo in a Southern church where Firth's good guy squares off against a congregation of brain-washed bigots, racists and homophobes, who apparently deserve to die in lurid close-up while Lynyrd Skynyrd's Free Bird strums on the soundtrack.

The film was cut by UK censors to secure a 15 certificate but I wouldn't want my nephews, if they were 15 or 16, anywhere near Vaughn's giddy bloodbath.

Gary Unwin (Taron Egerton), who is known to friends as Eggsy, is on a downward spiral despite an impressive IQ.

He is powerless to stop his mother Michelle (Samantha Womack) suffering abuse from her boyfriend (Geoff Bell), and a spot of joy-riding leads to a brief stay in a police cell.

Eggsy is dismissed as a hopeless cause by everyone except dapper secret agent Harry Hart (Colin Firth), who believes the young man has untapped potential as a crime-fighter.

So Hart enrols Eggsy in a gruelling training programme against sneering posh lads Charlie (Edward Holcroft), Barnaby (Matthew William Jones) and Hugo (Tom Prior), and friendlier rivals Grace (Sophie Cookson) and Roxy (Alisha Heng).

The recruits test their strength and guile in a series of challenges devised by gadget geek Merlin (Mark Strong).

Against the odds, Eggsy shines brighter than some of the supposed creme de la creme and when technological wizard Valentine (Samuel L Jackson) and his blade runner henchwoman Gazelle (Sofia Boutella) threaten mankind with a radical solution to climate change, Eggsy puts his training to good use alongside his stiff upper-lipped mentor.

Kingsman: The Secret Service leaves an exceedingly nasty taste in the mouth that is difficult to shake, garnished with crude sexism in the closing frames.

Firth is a debonair action hero, contrasting sharply with Egerton's bad boy from the wrong side of the tracks.

Jackson has fun with his lisping megalomaniac, who gags at the sight of blood.

If we did the same watching Vaughn's undeniably stylish film, we'd all need urgent medical assistance inside the first 20 minutes.